Method for uplink transmission and reception in wireless communication system and apparatus therefor

ABSTRACT

Performing uplink reception by a base station (BS) in a wireless communication system. In some implementations, a method includes: transmitting configuration information for a first sounding reference signal (SRS) that specifies a relation between the first SRS and a second SRS that is a reference for spatial beamforming of the first SRS, and based on the configuration information, receiving the first SRS which is transmitted by applying, to the first SRS, a first spatial beamforming that is identical to a second spatial beamforming used for transmission of the second SRS. The method further includes transmitting downlink control information (DCI) for uplink scheduling, where the DCI includes a SRS resource indication (SRI) and where a SRI field in the DCI carries the SRI, and where a bit width of the SRI field is based on a number of SRS resources in an SRS resource set configured for a user equipment (UE).

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.16/291,459, filed on Mar. 4, 2019, now allowed, which is a continuationof U.S. application Ser. No. 16/065,724, filed on Jun. 22, 2018, whichis the National Stage filing under 35 U.S.C. 371 of InternationalApplication No. PCT/KR2018/000367, filed on Jan. 8, 2018, which claimsthe benefit of U.S. Provisional Application No. 62/443,790, filed onJan. 8, 2017, No. 62/447,407, filed on Jan. 17, 2017, No. 62/457,985,filed on Feb. 12, 2017, No. 62/458,593, filed on Feb. 14, 2017, No.62/481,672, filed on Apr. 4, 2017, No. 62/592,339, filed on Nov. 29,2017, the contents of which are all hereby incorporated by referenceherein in their entirety.

TECHNICAL FIELD

The present invention relates to a wireless communication system, andmore particularly, to an uplink multi input multi output (MIMO)transmission method and an apparatus for supporting the same.

BACKGROUND ART

Mobile communication systems have been developed to provide voiceservices, while guaranteeing user activity. Service coverage of mobilecommunication systems, however, has extended even to data services, aswell as voice services, and currently, an explosive increase in traffichas resulted in shortage of resource and user demand for a high speedservices, requiring advanced mobile communication systems.

The requirements of the next-generation mobile communication system mayinclude supporting huge data traffic, a remarkable increase in thetransfer rate of each user, the accommodation of a significantlyincreased number of connection devices, very low end-to-end latency, andhigh energy efficiency. To this end, various techniques, such as smallcell enhancement, dual connectivity, massive Multiple Input MultipleOutput (MIMO), in-band full duplex, non-orthogonal multiple access(NOMA), supporting super-wide band, and device networking, have beenresearched.

DISCLOSURE Technical Problem

An embodiment of the present invention provides a method for uplinkmulti input multi output (MIMO) transmission.

Further, an embodiment of the present invention proposes a method fortransmitting an uplink reference signal which becomes a base for uplinkmulti input multi output (MIMO) transmission and a method forcontrolling the same.

In addition, an embodiment of the present invention proposes a methodfor configuring downlink control information (DCI) for uplink MIMOtransmission.

Technical objects to be achieved by the present invention are notlimited to the aforementioned technical objects, and other technicalobjects not described above may be evidently understood by a personhaving ordinary skill in the art to which the present invention pertainsfrom the following description.

Technical Solution

In an aspect of the present invention, a method for performing uplinktransmission by a user equipment (UE) in a wireless communication systemincludes: receiving sounding reference signal (SRS) resourceconfiguration information form a base station, in which the SRS resourceconfiguration information includes SRS resource information andassociation configuration information between a first SRS and a secondSRS that is a target of the SRS resource configuration information; andtransmitting precoded the second SRS to the base station on an SRSresource indicated by the SRS resource information, and the second SRSmay be transmitted based on the precoding applied to the first SRSindicated by the association configuration information.

In another aspect of the present invention, a user equipment (UE)performing uplink transmission in a wireless communication system,includes: a radio frequency (RF) unit for transmitting and receiving aradio signal; and a processor for controlling the RF unit, and theprocessor may be configured to receive sounding reference signal (SRS)resource configuration information form a base station, the SRS resourceconfiguration information in which SRS resource information andassociation configuration information between a first SRS and a secondSRS that is a target of the SRS resource configuration information, andtransmit precoded the second SRS to the base station on an SRS resourceindicated by the SR resource information, and the second SRS may betransmitted based on the precoding applied to the first SRS indicated bythe association configuration information.

Preferably, as the association configuration information, resourceinformation of the first SRS may be indicated or antenna portinformation on a resource of the first SRS may be indicated.

Preferably, for which operation the SRS resource is used may beconfigured by the base station.

Preferably, the operation may include an uplink data schedulingoperation and a beam management operation.

Preferably, a precoding may be applied to a SRS resource for the uplinkdata scheduling operation so as to form beams of the same direction inall SRS antenna ports configured in a single SRS resource.

Preferably, a precoding may be applied to a SRS resource for the beammanagement operation so as to form beams of different directions foreach SRS antenna port configured in a single SRS resource.

Preferably, the second SRS may be periodically transmitted oraperiodically transmitted by triggering by downlink control information(DCI).

Preferably, the first SRS may be an SRS latest transmitted beforetransmitting the second SRS.

Preferably, the downlink control information (DCI) for uplinkscheduling, which includes an SRS resource indication (SRI) may bereceived from the base station.

Preferably, a bit width of an SRI field carrying the SRI may bedetermined based on a number of SRS resources in an SRS resource setconfigured to the UE and a maximum number of layers supported for uplinktransmission.

Preferably, the bit width of the SRI field may be determined accordingto an equation below.ceil(log 2(S_tot))  [Equation]

Where ceil{x} represents a function that outputs the smallest integernot smaller than x,

${S_{tot} = {\sum\limits_{k = 1}^{L_{\max}}\;\begin{pmatrix}N \\k\end{pmatrix}}},$N represents a number of SRS resources in the SRS resource setconfigured to the UE, and L_max represents a maximum number of layerssupported for uplink transmission.

Preferably, the SRS resource set for determining the bit width of theSRI field may be implicitly determined or configured by the basestation.

Preferably, uplink may be transmitted on an SRS antenna port transmittedin a SRS resource selected by the SRI.

Preferably, when the uplink transmission is performed based on anon-codebook, the bit width of the SRI field carrying the SRI may bedetermined as the number of SRS resources in the SRS resource setconfigured to the UE and the maximum number of layers supported for theuplink transmission.

Advantageous Effects

According to the embodiment of the present invention, frequencyselective optimized precoding may be supported even in the uplink.

Further, according to the embodiment of the present invention, uplinktransmission throughput may be enhanced by applying optimized precodingfor each uplink subband (resource block group).

Further, according to the embodiment of the present invention, overheadof downlink control information related with the uplink for applyinguplink subband (resource block group) precoding may be minimized.

Effects which may be obtained by the present invention are not limitedto the aforementioned effects, and other technical effects not describedabove may be evidently understood by a person having ordinary skill inthe art to which the present invention pertains from the followingdescription.

DESCRIPTION OF DRAWINGS

The accompanying drawings, which are included herein as a part of thedescription for help understanding the present invention, provideembodiments of the present invention, and describe the technicalfeatures of the present invention with the description below.

FIG. 1A illustrates the radio frame structure type 1 in a wirelesscommunication system to which the present invention may be applied. FIG.1B illustrates the radio frame structure type 2 in a wirelesscommunication system to which the present invention may be applied.

FIG. 2 is a diagram illustrating a resource grid for a downlink slot ina wireless communication system to which the present invention may beapplied.

FIG. 3 illustrates a structure of downlink subframe in a wirelesscommunication system to which the present invention may be applied.

FIG. 4 illustrates a structure of uplink subframe in a wirelesscommunication system to which the present invention may be applied.

FIG. 5 shows the configuration of a known MIMO communication system.

FIG. 6 is a diagram showing a channel from a plurality of transmissionantennas to a single reception antenna.

FIG. 7A illustrates reference signal patterns mapped to downlinkresource block pair having a length of 14 OFDM symbols in a wirelesscommunication system to which the present invention may be applied. FIG.7B illustrates reference signal patterns mapped to downlink resourceblock pair having a length of 12 OFDM symbols in a wirelesscommunication system to which the present invention may be applied.

FIG. 8A shows twenty types of CSI-RS configurations available for CSI-RStransmission by one or two CSI-RS antenna ports, FIG. 8B shows ten typesof CSI-RS configurations available for four CSI-RS antenna ports, andFIG. 8C shows five types of CSI-RS configurations available for eightCSI-RS antenna port.

FIG. 9 illustrates an uplink subframe including a sounding referencesignal symbol in a wireless communication system to which the presentinvention may be applied.

FIG. 10 is a diagram illustrating a self-contained subframe structure inthe wireless communication system to which the present invention may beapplied.

FIG. 11A and FIG. 11B illustrate a transceiver unit model in thewireless communication system to which the present invention may beapplied. FIG. 11A illustrates a TXRU virtualization model which is TXRUvirtualization model option-1 and a sub-array partition model. FIG. 11Billustrates a TXRU virtualization model which is TXRU virtualizationmodel option-2 and a full-connection model model.

FIG. 12A is a diagram illustrating a service area for each transceiverunit in cased of all TXRUs having same beamforming direction. FIG. 12Bis a diagram illustrating a service area for each transceiver unit, asan example of spatial division multiplexing(SDM). FIG. 12C is a diagramillustrating a service area for each transceiver unit, as an example offrequency division multiplexing(FDM).

FIG. 13 is a diagram illustrating a method for transmitting andreceiving an uplink according to an embodiment of the present invention.

FIG. 14 is a diagram illustrating a method for transmitting andreceiving an uplink according to an embodiment of the present invention.

FIG. 15 illustrates a block diagram of a wireless communicationapparatus according to an embodiment of the present invention.

MODE FOR INVENTION

Some embodiments of the present invention are described in detail withreference to the accompanying drawings. A detailed description to bedisclosed along with the accompanying drawings are intended to describesome embodiments of the present invention and are not intended todescribe a sole embodiment of the present invention. The followingdetailed description includes more details in order to provide fullunderstanding of the present invention. However, those skilled in theart will understand that the present invention may be implementedwithout such more details.

In some cases, in order to avoid that the concept of the presentinvention becomes vague, known structures and devices are omitted or maybe shown in a block diagram form based on the core functions of eachstructure and device.

In this specification, a base station has the meaning of a terminal nodeof a network over which the base station directly communicates with adevice. In this document, a specific operation that is described to beperformed by a base station may be performed by an upper node of thebase station according to circumstances. That is, it is evident that ina network including a plurality of network nodes including a basestation, various operations performed for communication with a devicemay be performed by the base station or other network nodes other thanthe base station. The base station (BS) may be substituted with anotherterm, such as a fixed station, a Node B, an eNB (evolved-NodeB), a BaseTransceiver System (BTS), or an access point (AP). Furthermore, thedevice may be fixed or may have mobility and may be substituted withanother term, such as User Equipment (UE), a Mobile Station (MS), a UserTerminal (UT), a Mobile Subscriber Station (MSS), a Subscriber Station(SS), an Advanced Mobile Station (AMS), a Wireless Terminal (WT), aMachine-Type Communication (MTC) device, a Machine-to-Machine (M2M)device, or a Device-to-Device (D2D) device.

Hereinafter, downlink (DL) means communication from an eNB to UE, anduplink (UL) means communication from UE to an eNB. In DL, a transmittermay be part of an eNB, and a receiver may be part of UE. In UL, atransmitter may be part of UE, and a receiver may be part of an eNB.

Specific terms used in the following description have been provided tohelp understanding of the present invention, and the use of suchspecific terms may be changed in various forms without departing fromthe technical sprit of the present invention.

The following technologies may be used in a variety of wirelesscommunication systems, such as Code Division Multiple Access (CDMA),Frequency Division Multiple Access (FDMA), Time Division Multiple Access(TDMA), Orthogonal Frequency Division Multiple Access (OFDMA), SingleCarrier Frequency Division Multiple Access (SC-FDMA), and Non-OrthogonalMultiple Access (NOMA). CDMA may be implemented using a radiotechnology, such as Universal Terrestrial Radio Access (UTRA) orCDMA2000. TDMA may be implemented using a radio technology, such asGlobal System for Mobile communications (GSM)/General Packet RadioService (GPRS)/Enhanced Data rates for GSM Evolution (EDGE). OFDMA maybe implemented using a radio technology, such as Institute of Electricaland Electronics Engineers (IEEE) 802.11 (Wi-Fi), IEEE 802.16 (WiMAX),IEEE 802.20, or Evolved UTRA (E-UTRA). UTRA is part of a UniversalMobile Telecommunications System (UMTS). 3rd Generation PartnershipProject (3GPP) Long Term Evolution (LTE) is part of an Evolved UMTS(E-UMTS) using evolved UMTS Terrestrial Radio Access (E-UTRA), and itadopts OFDMA in downlink and adopts SC-FDMA in uplink. LTE-Advanced(LTE-A) is the evolution of 3GPP LTE.

Embodiments of the present invention may be supported by the standarddocuments disclosed in at least one of IEEE 802, 3GPP, and 3GPP2, thatis, radio access systems. That is, steps or portions that belong to theembodiments of the present invention and that are not described in orderto clearly expose the technical spirit of the present invention may besupported by the documents. Furthermore, all terms disclosed in thisdocument may be described by the standard documents.

In order to more clarify a description, 3GPP LTE/LTE-A or new RAT(RAT in5G(5 generation) system) is chiefly described, but the technicalcharacteristics of the present invention are not limited thereto.

General System to which the Present Invention May be Applied

FIG. 1A and FIG. 1B show the structure of a radio frame in a wirelesscommunication system to which an embodiment of the present invention maybe applied.

3GPP LTE/LTE-A support a radio frame structure type 1 which may beapplicable to Frequency Division Duplex (FDD) and a radio framestructure which may be applicable to Time Division Duplex (TDD).

The size of a radio frame in the time domain is represented as amultiple of a time unit of T_s=1/(15000*2048). A UL and DL transmissionincludes the radio frame having a duration of T_f=307200*T_s=10 ms.

FIG. 1A exemplifies a radio frame structure type 1. The type 1 radioframe may be applied to both of full duplex FDD and half duplex FDD.

A radio frame includes 10 subframes. A radio frame includes 20 slots ofT_slot=15360*T_s=0.5 ms length, and 0 to 19 indexes are given to each ofthe slots. One subframe includes consecutive two slots in the timedomain, and subframe i includes slot 2i and slot 2i+1. The time requiredfor transmitting a subframe is referred to as a transmission timeinterval (TTI). For example, the length of the subframe i may be 1 msand the length of a slot may be 0.5 ms.

A UL transmission and a DL transmission I the FDD are distinguished inthe frequency domain. Whereas there is no restriction in the full duplexFDD, a UE may not transmit and receive simultaneously in the half duplexFDD operation.

One slot includes a plurality of Orthogonal Frequency DivisionMultiplexing (OFDM) symbols in the time domain and includes a pluralityof Resource Blocks (RBs) in a frequency domain. In 3GPP LTE, OFDMsymbols are used to represent one symbol period because OFDMA is used indownlink. An OFDM symbol may be called one SC-FDMA symbol or symbolperiod. An RB is a resource allocation unit and includes a plurality ofcontiguous subcarriers in one slot.

FIG. 1B shows frame structure type 2.

A type 2 radio frame includes two half frame of 153600*T_s=5 ms lengtheach. Each half frame includes 5 subframes of 30720*T_s=1 ms length.

In the frame structure type 2 of a TDD system, an uplink-downlinkconfiguration is a rule indicating whether uplink and downlink areallocated (or reserved) to all subframes.

Table 1 shows the uplink-downlink configuration.

TABLE 1 Downlink- to-Uplink Uplink- Switch- Downlink point Subframenumber configuration periodicity 0 1 2 3 4 5 6 7 8 9 0 5 ms D S U U U DS U U U 1 5 ms D S U U D D S U U D 2 5 ms D S U D D D S U D D 3 10 ms DS U U U D D D D D 4 10 ms D S U U D D D D D D 5 10 ms D S U D D D D D DD 6 5 ms D S U U U D S U U D

Referring to Table 1, in each subframe of the radio frame, ‘D’represents a subframe for a DL transmission, ‘U’ represents a subframefor UL transmission, and ‘S’ represents a special subframe includingthree types of fields including a Downlink Pilot Time Slot (DwPTS), aGuard Period (GP), and a Uplink Pilot Time Slot (UpPTS).

A DwPTS is used for an initial cell search, synchronization or channelestimation in a UE. A UpPTS is used for channel estimation in an eNB andfor synchronizing a UL transmission synchronization of a UE. A GP isduration for removing interference occurred in a UL owing to multi-pathdelay of a DL signal between a UL and a DL.

Each subframe i includes slot 2i and slot 2i+1 of T_slot=15360*T_s=0.5ms.

The UL-DL configuration may be classified into 7 types, and the positionand/or the number of a DL subframe, a special subframe and a UL subframeare different for each configuration.

A point of time at which a change is performed from downlink to uplinkor a point of time at which a change is performed from uplink todownlink is called a switching point. The periodicity of the switchingpoint means a cycle in which an uplink subframe and a downlink subframeare changed is identically repeated. Both 5 ms and 10 ms are supportedin the periodicity of a switching point. If the periodicity of aswitching point has a cycle of a 5 ms downlink-uplink switching point,the special subframe S is present in each half frame. If the periodicityof a switching point has a cycle of a 5 ms downlink-uplink switchingpoint, the special subframe S is present in the first half frame only.

In all the configurations, 0 and 5 subframes and a DwPTS are used foronly downlink transmission. An UpPTS and a subframe subsequent to asubframe are always used for uplink transmission.

Such uplink-downlink configurations may be known to both an eNB and UEas system information. An eNB may notify UE of a change of theuplink-downlink allocation state of a radio frame by transmitting onlythe index of uplink-downlink configuration information to the UEwhenever the uplink-downlink configuration information is changed.Furthermore, configuration information is kind of downlink controlinformation and may be transmitted through a Physical Downlink ControlChannel (PDCCH) like other scheduling information. Configurationinformation may be transmitted to all UEs within a cell through abroadcast channel as broadcasting information.

Table 2 represents configuration (length of DwPTS/GP/UpPTS) of a specialsubframe.

TABLE 2 Normal cyclic prefix in downlink Extended cyclic prefix indownlink UpPTS UpPTS Special Normal Extended Normal Extended subframecyclic prefix cyclic prefix cyclic prefix cyclic prefix configurationDwPTS in uplink in uplink DwPTS in uplink in uplink 0  6592 · T_(s) 2192· T_(s) 2560 · T_(s)  7680 · T_(s) 2192 · T_(s) 2560 · T_(s) 1 19760 ·T_(s) 20480 · T_(s) 2 21952 · T_(s) 23040 · T_(s) 3 24144 · T_(s) 25600· T_(s) 4 26336 · T_(s)  7680 · T_(s) 4384 · T_(s) 5120 · T_(s) 5  6592· T_(s) 4384 · T_(s) 5120 · T_(s) 20480 · T_(s) 6 19760 · T_(s) 23040 ·T_(s) 7 21952 · T_(s) — — — 8 24144 · T_(s) — — —

The structure of a radio subframe according to the example of FIG. 1Aand FIG. 1B is just an example, and the number of subcarriers includedin a radio frame, the number of slots included in a subframe and thenumber of OFDM symbols included in a slot may be changed in variousmanners.

FIG. 2 is a diagram illustrating a resource grid for one downlink slotin a wireless communication system to which an embodiment of the presentinvention may be applied.

Referring to FIG. 2, one downlink slot includes a plurality of OFDMsymbols in a time domain. It is described herein that one downlink slotincludes 7 OFDMA symbols and one resource block includes 12 subcarriersfor exemplary purposes only, and the present invention is not limitedthereto.

Each element on the resource grid is referred to as a resource element,and one resource block (RB) includes 12×7 resource elements. The numberof RBs N{circumflex over ( )}DL included in a downlink slot depends on adownlink transmission bandwidth.

The structure of an uplink slot may be the same as that of a downlinkslot.

FIG. 3 shows the structure of a downlink subframe in a wirelesscommunication system to which an embodiment of the present invention maybe applied.

Referring to FIG. 3, a maximum of three OFDM symbols located in a frontportion of a first slot of a subframe correspond to a control region inwhich control channels are allocated, and the remaining OFDM symbolscorrespond to a data region in which a physical downlink shared channel(PDSCH) is allocated. Downlink control channels used in 3GPP LTEinclude, for example, a physical control format indicator channel(PCFICH), a physical downlink control channel (PDCCH), and a physicalhybrid-ARQ indicator channel (PHICH).

A PCFICH is transmitted in the first OFDM symbol of a subframe andcarries information about the number of OFDM symbols (i.e., the size ofa control region) which is used to transmit control channels within thesubframe. A PHICH is a response channel for uplink and carries anacknowledgement (ACK)/not-acknowledgement (NACK) signal for a HybridAutomatic Repeat Request (HARQ). Control information transmitted in aPDCCH is called Downlink Control Information (DCI). DCI includes uplinkresource allocation information, downlink resource allocationinformation, or an uplink transmission (Tx) power control command for aspecific UE group.

A PDCCH may carry information about the resource allocation andtransport format of a downlink shared channel (DL-SCH) (this is alsocalled an “downlink grant”), resource allocation information about anuplink shared channel (UL-SCH) (this is also called a “uplink grant”),paging information on a PCH, system information on a DL-SCH, theresource allocation of a higher layer control message, such as a randomaccess response transmitted on a PDSCH, a set of transmission powercontrol commands for individual UE within specific UE group, and theactivation of a Voice over Internet Protocol (VoIP), etc. A plurality ofPDCCHs may be transmitted within the control region, and UE may monitora plurality of PDCCHs. A PDCCH is transmitted on a single ControlChannel Element (CCE) or an aggregation of some contiguous CCEs. A CCEis a logical allocation unit that is used to provide a PDCCH with acoding rate according to the state of a radio channel. A CCE correspondsto a plurality of resource element groups. The format of a PDCCH and thenumber of available bits of a PDCCH are determined by an associationrelationship between the number of CCEs and a coding rate provided byCCEs.

An eNB determines the format of a PDCCH based on DCI to be transmittedto UE and attaches a Cyclic Redundancy Check (CRC) to controlinformation. A unique identifier (a Radio Network Temporary Identifier(RNTI)) is masked to the CRC depending on the owner or use of a PDCCH.If the PDCCH is a PDCCH for specific UE, an identifier unique to the UE,for example, a Cell-RNTI (C-RNTI) may be masked to the CRC. If the PDCCHis a PDCCH for a paging message, a paging indication identifier, forexample, a Paging-RNTI (P-RNTI) may be masked to the CRC. If the PDCCHis a PDCCH for system information, more specifically, a SystemInformation Block (SIB), a system information identifier, for example, aSystem Information-RNTI (SI-RNTI) may be masked to the CRC. A RandomAccess-RNTI (RA-RNTI) may be masked to the CRC in order to indicate arandom access response which is a response to the transmission of arandom access preamble by UE.

FIG. 4 shows the structure of an uplink subframe in a wirelesscommunication system to which an embodiment of the present invention maybe applied.

Referring to FIG. 4, the uplink subframe may be divided into a controlregion and a data region in a frequency domain. A physical uplinkcontrol channel (PUCCH) carrying uplink control information is allocatedto the control region. A physical uplink shared channel (PUSCH) carryinguser data is allocated to the data region. In order to maintain singlecarrier characteristic, one UE does not send a PUCCH and a PUSCH at thesame time.

A Resource Block (RB) pair is allocated to a PUCCH for one UE within asubframe. RBs belonging to an RB pair occupy different subcarriers ineach of 2 slots. This is called that an RB pair allocated to a PUCCH isfrequency-hopped in a slot boundary.

Multi-Input Multi-Output (MIMO)

A MIMO technology does not use single transmission antenna and singlereception antenna that have been commonly used so far, but uses amulti-transmission (Tx) antenna and a multi-reception (Rx) antenna. Inother words, the MIMO technology is a technology for increasing acapacity or enhancing performance using multi-input/output antennas inthe transmission end or reception end of a wireless communicationsystem. Hereinafter, MIMO is called a “multi-input/output antenna.”.

More specifically, the multi-input/output antenna technology does notdepend on a single antenna path in order to receive a single totalmessage and completes total data by collecting a plurality of datapieces received through several antennas. As a result, themulti-input/output antenna technology can increase a data transfer ratewithin a specific system range and can also increase a system rangethrough a specific data transfer rate.

It is expected that an efficient multi-input/output antenna technologywill be used because next-generation mobile communication requires adata transfer rate much higher than that of existing mobilecommunication. In such a situation, the MIMO communication technology isa next-generation mobile communication technology which may be widelyused in mobile communication UE and a relay node and has been in thespotlight as a technology which may overcome a limit to the transferrate of another mobile communication attributable to the expansion ofdata communication.

Meanwhile, the multi-input/output antenna (MIMO) technology of varioustransmission efficiency improvement technologies that are beingdeveloped has been most in the spotlight as a method capable ofsignificantly improving a communication capacity andtransmission/reception performance even without the allocation ofadditional frequencies or a power increase.

FIG. 5 shows the configuration of a known MIMO communication system.

Referring to FIG. 5, if the number of transmission (Tx) antennas isincreased to N_T and the number of reception (Rx) antennas is increasedto N_R at the same time, a theoretical channel transmission capacity isincreased in proportion to the number of antennas, unlike in the casewhere a plurality of antennas is used only in a transmitter or areceiver. Accordingly, a transfer rate can be improved, and frequencyefficiency can be significantly improved. In this case, a transfer rateaccording to an increase of a channel transmission capacity may betheoretically increased by a value obtained by multiplying the followingrate increment R_i by a maximum transfer rate R_o if one antenna isused.R _(i)=min(N _(T) ,N _(R))  [Equation 1]

That is, in an MIMO communication system using 4 transmission antennasand 4 reception antennas, for example, a quadruple transfer rate can beobtained theoretically compared to a single antenna system.

Such a multi-input/output antenna technology may be divided into aspatial diversity method for increasing transmission reliability usingsymbols passing through various channel paths and a spatial multiplexingmethod for improving a transfer rate by sending a plurality of datasymbols at the same time using a plurality of transmission antennas.Furthermore, active research is being recently carried out on a methodfor properly obtaining the advantages of the two methods by combiningthe two methods.

Each of the methods is described in more detail below.

First, the spatial diversity method includes a space-time blockcode-series method and a space-time Trelis code-series method using adiversity gain and a coding gain at the same time. In general, theTrelis code-series method is better in terms of bit error rateimprovement performance and the degree of a code generation freedom,whereas the space-time block code-series method has low operationalcomplexity. Such a spatial diversity gain may correspond to an amountcorresponding to the product (N_T×N_R) of the number of transmissionantennas (N_T) and the number of reception antennas (N_R).

Second, the spatial multiplexing scheme is a method for sendingdifferent data streams in transmission antennas. In this case, in areceiver, mutual interference is generated between data transmitted by atransmitter at the same time. The receiver removes the interferenceusing a proper signal processing scheme and receives the data. A noiseremoval method used in this case may include a Maximum LikelihoodDetection (MLD) receiver, a Zero-Forcing (ZF) receiver, a Minimum MeanSquare Error (MMSE) receiver, Diagonal-Bell Laboratories LayeredSpace-Time (D-BLAST), and Vertical-Bell Laboratories Layered Space-Time(V-BLAST). In particular, if a transmission end can be aware of channelinformation, a Singular Value Decomposition (SVD) method may be used.

Third, there is a method using a combination of a spatial diversity andspatial multiplexing. If only a spatial diversity gain is to beobtained, a performance improvement gain according to an increase of adiversity disparity is gradually saturated. If only a spatialmultiplexing gain is used, transmission reliability in a radio channelis deteriorated. Methods for solving the problems and obtaining the twogains have been researched and may include a double space-time transmitdiversity (double-STTD) method and a space-time bit interleaved codedmodulation (STBICM).

In order to describe a communication method in a multi-input/outputantenna system, such as that described above, in more detail, thecommunication method may be represented as follows through mathematicalmodeling.

First, as shown in FIG. 5, it is assumed that N_T transmission antennasand NR reception antennas are present.

First, a transmission signal is described below. If the N_T transmissionantennas are present as described above, a maximum number of pieces ofinformation which can be transmitted are N_T, which may be representedusing the following vector.s=[s ₁ ,s ₂ , . . . ,s _(N) _(T) ]^(T)  [Equation 2]

Meanwhile, transmission power may be different in each of pieces oftransmission information s_1, s_2, . . . , s_NT. In this case, if piecesof transmission power are P_1, P_2, . . . , P_NT, transmissioninformation having controlled transmission power may be representedusing the following vector.ŝ=[ŝ ₁ ,ŝ ₂ , . . . ,ŝ _(N) _(T) ]^(T)=[P ₁ s ₁ ,P ₂ s ₂ , . . . ,P _(N)_(T) s _(N) _(T) ]^(T)  [Equation 3 ]

Furthermore, transmission information having controlled transmissionpower in the Equation 3 may be represented as follows using the diagonalmatrix P of transmission power.

$\begin{matrix}{\hat{s} = {{\begin{bmatrix}P_{1} & \; & \; & {0\mspace{31mu}} \\\; & P_{2} & \; & \; \\\; & \; & \ddots & \; \\{0\mspace{14mu}} & \; & \; & P_{N_{T}}\end{bmatrix}\begin{bmatrix}{s_{1}\mspace{14mu}} \\{s_{2}\mspace{14mu}} \\{\vdots\mspace{31mu}} \\s_{N_{T}}\end{bmatrix}} = {Ps}}} & \lbrack {{Equation}\mspace{14mu} 4} \rbrack\end{matrix}$

Meanwhile, the information vector having controlled transmission powerin the Equation 4 is multiplied by a weight matrix W, thus forming N_Ttransmission signals x_1, x_2, . . . , x_NT that are actuallytransmitted. In this case, the weight matrix functions to properlydistribute the transmission information to antennas according to atransport channel condition. The following may be represented using thetransmission signals x_1, x_2, . . . , x_NT.

$\begin{matrix}{x = {\quad{\begin{bmatrix}{x_{1}\mspace{14mu}} \\{x_{2}\mspace{14mu}} \\{\vdots\mspace{34mu}} \\{x_{i}\mspace{20mu}} \\{\vdots\mspace{34mu}} \\x_{N_{T}}\end{bmatrix} = {{\begin{bmatrix}{w_{11}\mspace{14mu}} & {w_{12}\mspace{14mu}} & \cdots & {w_{1N_{T}}\mspace{14mu}} \\{w_{21}\mspace{14mu}} & {w_{22}\mspace{14mu}} & \cdots & {w_{2N_{T}}\mspace{14mu}} \\{\vdots\mspace{50mu}} & \; & \ddots & \; \\{w_{i\; 1}\mspace{20mu}} & {w_{i\; 2}\mspace{20mu}} & \cdots & {w_{{iN}_{T}}\mspace{20mu}} \\{\vdots\mspace{50mu}} & \; & \ddots & \; \\w_{N_{T}1} & w_{N_{T}2} & \cdots & w_{N_{T}N_{T}}\end{bmatrix}\begin{bmatrix}{{\hat{s}}_{1}\mspace{14mu}} \\{{\hat{s}}_{2}\mspace{14mu}} \\{\vdots\mspace{31mu}} \\{{\hat{s}}_{j}\mspace{14mu}} \\{\vdots\mspace{31mu}} \\{\hat{s}}_{N_{T}}\end{bmatrix}} = {{W\hat{s}} = {WPs}}}}}} & \lbrack {{Equation}\mspace{14mu} 5} \rbrack\end{matrix}$

In this case, w_ij denotes weight between an i-th transmission antennaand a j-th transmission information, and W is an expression of a matrixof the weight. Such a matrix W is called a weight matrix or precodingmatrix.

Meanwhile, the transmission signal x, such as that described above, maybe considered to be used in a case where a spatial diversity is used anda case where spatial multiplexing is used.

If spatial multiplexing is used, all the elements of the informationvector s have different values because different signals are multiplexedand transmitted. In contrast, if the spatial diversity is used, all theelements of the information vector s have the same value because thesame signals are transmitted through several channel paths.

A method of mixing spatial multiplexing and the spatial diversity may betaken into consideration. In other words, the same signals may betransmitted using the spatial diversity through 3 transmission antennas,for example, and the remaining different signals may be spatiallymultiplexed and transmitted.

If N_R reception antennas are present, the reception signals y_1, y_2, .. . , y_NR of the respective antennas are represented as follows using avector y.y=[y ₁ ,y ₂ , . . . ,y _(N) _(R) ]^(T)  [Equation 6]

Meanwhile, if channels in a multi-input/output antenna communicationsystem are modeled, the channels may be classified according totransmission/reception antenna indices. A channel passing through areception antenna i from a transmission antenna j is represented ash_ij. In this case, it is to be noted that in order of the index ofh_ij, the index of a reception antenna comes first and the index of atransmission antenna then comes.

Several channels may be grouped and expressed in a vector and matrixform. For example, a vector expression is described below.

FIG. 6 is a diagram showing a channel from a plurality of transmissionantennas to a single reception antenna.

As shown in FIG. 6, a channel from a total of N_T transmission antennasto a reception antenna i may be represented as follows.h _(i) ^(T)=[h _(i1) ,h _(i2) , . . . ,h _(iN) _(T) ]  [Equation 7]

Furthermore, if all channels from the N_T transmission antenna to NRreception antennas are represented through a matrix expression, such asEquation 7, they may be represented as follows.

$\begin{matrix}{H = {\begin{bmatrix}{h_{1}^{T}\mspace{14mu}} \\{h_{2}^{T}\mspace{14mu}} \\{\vdots\mspace{34mu}} \\{h_{i}^{T}\mspace{14mu}} \\{\vdots\mspace{34mu}} \\h_{N_{R}}^{T}\end{bmatrix} = \begin{bmatrix}{h_{11}\mspace{14mu}} & {h_{12}\mspace{14mu}} & \cdots & {h_{1N_{T}}\mspace{14mu}} \\{h_{21}\mspace{14mu}} & {h_{22}\mspace{14mu}} & \cdots & {h_{2N_{T}}\mspace{14mu}} \\{\vdots\mspace{45mu}} & \; & \ddots & \; \\{h_{i\; 1}\mspace{20mu}} & {h_{i\; 2}\mspace{20mu}} & \cdots & {h_{{iN}_{T}}\mspace{20mu}} \\{\vdots\mspace{45mu}} & \; & \ddots & \; \\h_{N_{R}1} & h_{N_{R}2} & \cdots & h_{N_{R}N_{T}}\end{bmatrix}}} & \lbrack {{Equation}\mspace{14mu} 8} \rbrack\end{matrix}$

Meanwhile, Additive White Gaussian Noise (AWGN) is added to an actualchannel after the actual channel experiences the channel matrix H.Accordingly, AWGN n_1, n_2, . . . , n_NR added to the N_R receptionantennas, respectively, are represented using a vector as follows.n=[n ₁ ,n ₂ , . . . ,n _(N) _(R) ]^(T)  [Equation 9]

A transmission signal, a reception signal, a channel, and AWGN in amulti-input/output antenna communication system may be represented tohave the following relationship through the modeling of the transmissionsignal, reception signal, channel, and AWGN, such as those describedabove.

$\begin{matrix}{y = {\quad{\begin{bmatrix}{y_{1}\mspace{14mu}} \\{y_{2}\mspace{14mu}} \\{\vdots\mspace{34mu}} \\{y_{i}\mspace{20mu}} \\{\vdots\mspace{34mu}} \\y_{N_{R}}\end{bmatrix} = {{{\begin{bmatrix}{h_{11}\mspace{14mu}} & {h_{12}\mspace{14mu}} & \cdots & {h_{1N_{T}}\mspace{14mu}} \\{h_{21}\mspace{14mu}} & {h_{22}\mspace{14mu}} & \cdots & {h_{2N_{T}}\mspace{14mu}} \\{\vdots\mspace{50mu}} & \; & \ddots & \; \\{h_{i\; 1}\mspace{20mu}} & {h_{i\; 2}\mspace{20mu}} & \cdots & {h_{{iN}_{T}}\mspace{20mu}} \\{\vdots\mspace{50mu}} & \; & \ddots & \; \\h_{N_{R}1} & h_{N_{R}2} & \cdots & h_{N_{R}N_{T}}\end{bmatrix}\begin{bmatrix}{x_{1}\mspace{14mu}} \\{x_{2}\mspace{14mu}} \\{\vdots\mspace{31mu}} \\{x_{j}\mspace{14mu}} \\{\vdots\mspace{31mu}} \\x_{N_{T}}\end{bmatrix}} + \begin{bmatrix}{n_{1}\mspace{14mu}} \\{n_{2}\mspace{14mu}} \\{\vdots\mspace{31mu}} \\{n_{i}\mspace{14mu}} \\{\vdots\mspace{31mu}} \\n_{N_{R}}\end{bmatrix}} = {{Hx} + n}}}}} & \lbrack {{Equation}\mspace{14mu} 10} \rbrack\end{matrix}$

Meanwhile, the number of rows and columns of the channel matrix Hindicative of the state of channels is determined by the number oftransmission/reception antennas. In the channel matrix H, as describedabove, the number of rows becomes equal to the number of receptionantennas N_R, and the number of columns becomes equal to the number oftransmission antennas N_T. That is, the channel matrix H becomes anN_R×N_T matrix.

In general, the rank of a matrix is defined as a minimum number of thenumber of independent rows or columns. Accordingly, the rank of thematrix is not greater than the number of rows or columns. As for figuralstyle, for example, the rank H of the channel matrix H is limited asfollows.rank(H)≤min(N _(T) ,N _(R))  [Equation 11]

Furthermore, if a matrix is subjected to Eigen value decomposition, arank may be defined as the number of Eigen values that belong to Eigenvalues and that are not 0. Likewise, if a rank is subjected to SingularValue Decomposition (SVD), it may be defined as the number of singularvalues other than 0. Accordingly, the physical meaning of a rank in achannel matrix may be said to be a maximum number on which differentinformation may be transmitted in a given channel.

In this specification, a “rank” for MIMO transmission indicates thenumber of paths through which signals may be independently transmittedat a specific point of time and a specific frequency resource. The“number of layers” indicates the number of signal streams transmittedthrough each path. In general, a rank has the same meaning as the numberof layers unless otherwise described because a transmission end sendsthe number of layers corresponding to the number of ranks used in signaltransmission.

Reference Signal (RS)

In a wireless communication system, a signal may be distorted duringtransmission because data is transmitted through a radio channel. Inorder for a reception end to accurately receive a distorted signal, thedistortion of a received signal needs to be corrected using channelinformation. In order to detect channel information, a method ofdetecting channel information using the degree of the distortion of asignal transmission method and a signal known to both the transmissionside and the reception side when they are transmitted through a channelis chiefly used. The aforementioned signal is called a pilot signal orreference signal (RS).

Furthermore recently, when most of mobile communication systems transmita packet, they use a method capable of improving transmission/receptiondata efficiency by adopting multiple transmission antennas and multiplereception antennas instead of using one transmission antenna and onereception antenna used so far. When data is transmitted and receivedusing multiple input/output antennas, a channel state between thetransmission antenna and the reception antenna must be detected in orderto accurately receive the signal. Accordingly, each transmission antennamust have an individual reference signal.

In a mobile communication system, an RS may be basically divided intotwo types depending on its object. There are an RS having an object ofobtaining channel state information and an RS used for datademodulation. The former has an object of obtaining, by a UE, to obtainchannel state information in the downlink. Accordingly, a correspondingRS must be transmitted in a wideband, and a UE must be capable ofreceiving and measuring the RS although the UE does not receive downlinkdata in a specific subframe. Furthermore, the former is also used forradio resources management (RRM) measurement, such as handover. Thelatter is an RS transmitted along with corresponding resources when aneNB transmits the downlink. A UE may perform channel estimation byreceiving a corresponding RS and thus may demodulate data. Thecorresponding RS must be transmitted in a region in which data istransmitted.

A downlink RS includes one common RS (CRS) for the acquisition ofinformation about a channel state shared by all of UEs within a cell andmeasurement, such as handover, and a dedicated RS (DRS) used for datademodulation for only a specific UE. Information for demodulation andchannel measurement can be provided using such RSs. That is, the DRS isused for only data demodulation, and the CRS is used for the two objectsof channel information acquisition and data demodulation.

The reception side (i.e., UE) measures a channel state based on a CRSand feeds an indicator related to channel quality, such as a channelquality indicator (CQI), a precoding matrix index (PMI) and/or a rankindicator (RI), back to the transmission side (i.e., an eNB). The CRS isalso called a cell-specific RS. In contrast, a reference signal relatedto the feedback of channel state information (CSI) may be defined as aCSI-RS.

The DRS may be transmitted through resource elements if data on a PDSCHneeds to be demodulated. A UE may receive information about whether aDRS is present through a higher layer, and the DRS is valid only if acorresponding PDSCH has been mapped. The DRS may also be called aUE-specific RS or demodulation RS (DMRS).

FIG. 7A and FIG. 7B illustrate reference signal patterns mapped todownlink resource block pairs in a wireless communication system towhich the present invention may be applied.

Referring to FIG. 7A and FIG. 7B, a downlink resource block pair, thatis, a unit in which a reference signal is mapped, may be represented inthe form of one subframe in a time domain X 12 subcarriers in afrequency domain. That is, in a time axis (an x axis), one resourceblock pair has a length of 14 OFDM symbols in the case of a normalcyclic prefix (CP) (FIG. 7A) and has a length of 12 OFDM symbols in thecase of an extended cyclic prefix (CP) (FIG. 7B). In the resource blocklattice, resource elements (REs) indicated by “0”, “1”, “2”, and “3”mean the locations of the CRSs of antenna port indices “0”, “1”, “2”,and “3”, respectively, and REs indicated by “D” mean the location of aDRS.

A CRS is described in more detail below. The CRS is a reference signalwhich is used to estimate the channel of a physical antenna and may bereceived by all UEs located within a cell in common. The CRS isdistributed to a full frequency bandwidth. That is, the CRS iscell-specific signal and is transmitted every subframe in a wideband.Furthermore, the CRS may be used for channel quality information (CSI)and data demodulation.

A CRS is defined in various formats depending on an antenna array on thetransmitting side (eNB). In the 3GPP LTE system (e.g., Release-8), an RSfor a maximum four antenna ports is transmitted depending on the numberof transmission antennas of an eNB. The side from which a downlinksignal is transmitted has three types of antenna arrays, such as asingle transmission antenna, two transmission antennas and fourtransmission antennas. For example, if the number of transmissionantennas of an eNB is two, CRSs for a No. 0 antenna port and a No. 1antenna port are transmitted. If the number of transmission antennas ofan eNB is four, CRSs for No. 0˜No. 3 antenna ports are transmitted. Ifthe number of transmission antennas of an eNB is four, a CRS pattern inone RB is shown in FIG. 7A and FIG. 7B.

If an eNB uses a single transmission antenna, reference signals for asingle antenna port are arrayed.

If an eNB uses two transmission antennas, reference signals for twotransmission antenna ports are arrayed using a time divisionmultiplexing (TDM) scheme and/or a frequency division multiplexing (FDM)scheme. That is, different time resources and/or different frequencyresources are allocated in order to distinguish between referencesignals for two antenna ports.

Furthermore, if an eNB uses four transmission antennas, referencesignals for four transmission antenna ports are arrayed using the TDMand/or FDM schemes. Channel information measured by the reception side(i.e., UE) of a downlink signal may be used to demodulate datatransmitted using a transmission scheme, such as single transmissionantenna transmission, transmission diversity, closed-loop spatialmultiplexing, open-loop spatial multiplexing or amulti-user-multi-input/output (MIMO) antenna.

If a multi-input multi-output antenna is supported, when a RS istransmitted by a specific antenna port, the RS is transmitted in thelocations of resource elements specified depending on a pattern of theRS and is not transmitted in the locations of resource elementsspecified for other antenna ports. That is, RSs between differentantennas do not overlap.

A DRS is described in more detail below. The DRS is used to demodulatedata. In multi-input multi-output antenna transmission, precoding weightused for a specific UE is combined with a transmission channeltransmitted by each transmission antenna when the UE receives an RS, andis used to estimate a corresponding channel without any change.

A 3GPP LTE system (e.g., Release-8) supports a maximum of fourtransmission antennas, and a DRS for rank 1 beamforming is defined. TheDRS for rank 1 beamforming also indicates an RS for an antenna portindex 5.

In an LTE-A system, that is, an advanced and developed form of the LTEsystem, the design is necessary to support a maximum of eighttransmission antennas in the downlink of an eNB. Accordingly, RSs forthe maximum of eight transmission antennas must be also supported. Inthe LTE system, only downlink RSs for a maximum of four antenna portshas been defined. Accordingly, if an eNB has four to a maximum of eightdownlink transmission antennas in the LTE-A system, RSs for theseantenna ports must be additionally defined and designed. Regarding theRSs for the maximum of eight transmission antenna ports, theaforementioned RS for channel measurement and the aforementioned RS fordata demodulation must be designed.

One of important factors that must be considered in designing an LTE-Asystem is backward compatibility, that is, that an LTE UE must welloperate even in the LTE-A system, which must be supported by the system.From an RS transmission viewpoint, in the time-frequency domain in whicha CRS defined in LTE is transmitted in a full band every subframe, RSsfor a maximum of eight transmission antenna ports must be additionallydefined. In the LTE-A system, if an RS pattern for a maximum of eighttransmission antennas is added in a full band every subframe using thesame method as the CRS of the existing LTE, RS overhead is excessivelyincreased.

Accordingly, the RS newly designed in the LTE-A system is basicallydivided into two types, which include an RS having a channel measurementobject for the selection of MCS or a PMI (channel state information-RSor channel state indication-RS (CSI-RS)) and an RS for the demodulationof data transmitted through eight transmission antennas (datademodulation-RS (DM-RS)).

The CSI-RS for the channel measurement object is characterized in thatit is designed for an object focused on channel measurement unlike theexisting CRS used for objects for measurement, such as channelmeasurement and handover, and for data demodulation. Furthermore, theCSI-RS may also be used for an object for measurement, such as handover.The CSI-RS does not need to be transmitted every subframe unlike the CRSbecause it is transmitted for an object of obtaining information about achannel state. In order to reduce overhead of a CSI-RS, the CSI-RS isintermittently transmitted on the time axis.

For data demodulation, a DM-RS is dedicatedly transmitted to a UEscheduled in a corresponding time-frequency domain. That is, a DM-RS fora specific UE is transmitted only in a region in which the correspondingUE has been scheduled, that is, in the time-frequency domain in whichdata is received.

In the LTE-A system, a maximum of eight transmission antennas aresupported in the downlink of an eNB. In the LTE-A system, if RSs for amaximum of eight transmission antennas are transmitted in a full bandevery subframe using the same method as the CRS in the existing LTE, RSoverhead is excessively increased. Accordingly, in the LTE-A system, anRS has been separated into the CSI-RS of the CSI measurement object forthe selection of MCS or a PMI and the DM-RS for data demodulation, andthus the two RSs have been added. The CSI-RS may also be used for anobject, such as RRM measurement, but has been designed for a main objectfor the acquisition of CSI. The CSI-RS does not need to be transmittedevery subframe because it is not used for data demodulation.Accordingly, in order to reduce overhead of the CSI-RS, the CSI-RS isintermittently transmitted on the time axis. That is, the CSI-RS has aperiod corresponding to a multiple of the integer of one subframe andmay be periodically transmitted or transmitted in a specifictransmission pattern. In this case, the period or pattern in which theCSI-RS is transmitted may be set by an eNB.

For data demodulation, a DM-RS is dedicatedly transmitted to a UEscheduled in a corresponding time-frequency domain. That is, a DM-RS fora specific UE is transmitted only in the region in which scheduling isperformed for the corresponding UE, that is, only in the time-frequencydomain in which data is received.

In order to measure a CSI-RS, a UE must be aware of information aboutthe transmission subframe index of the CSI-RS for each CSI-RS antennaport of a cell to which the UE belongs, the location of a CSI-RSresource element (RE) time-frequency within a transmission subframe, anda CSI-RS sequence.

In the LTE-A system, an eNB has to transmit a CSI-RS for each of amaximum of eight antenna ports. Resources used for the CSI-RStransmission of different antenna ports must be orthogonal. When one eNBtransmits CSI-RSs for different antenna ports, it may orthogonallyallocate the resources according to the FDM/TDM scheme by mapping theCSI-RSs for the respective antenna ports to different REs.Alternatively, the CSI-RSs for different antenna ports may betransmitted according to the CDM scheme for mapping the CSI-RSs topieces of code orthogonal to each other.

When an eNB notifies a UE belonging to the eNB of information on aCSI-RS, first, the eNB must notify the UE of information about atime-frequency in which a CSI-RS for each antenna port is mapped.Specifically, the information includes subframe numbers in which theCSI-RS is transmitted or a period in which the CSI-RS is transmitted, asubframe offset in which the CSI-RS is transmitted, an OFDM symbolnumber in which the CSI-RS RE of a specific antenna is transmitted,frequency spacing, and the offset or shift value of an RE in thefrequency axis.

A CSI-RS is transmitted through one, two, four or eight antenna ports.Antenna ports used in this case are p=15, p=15, 16, p=15, . . . , 18,and p=15, . . . , 22, respectively. A CSI-RS may be defined for only asubcarrier interval Δf=15 kHz.

In a subframe configured for CSI-RS transmission, a CSI-RS sequence ismapped to a complex-valued modulation symbol a_k,l{circumflex over( )}(p) used as a reference symbol on each antenna port p as in Equation12.

$\begin{matrix}{{a_{k,l}^{(p)} = {w_{l^{''} \cdot}~{r_{l,n_{s}}( m^{\prime} )}}}{k = {k^{\prime} + {12m} + \{ {{\begin{matrix}{- 0} & {{{{{for}\mspace{14mu} p} \in \{ {15,16} \}},{{normal}\mspace{14mu}{cyclic}\mspace{14mu}{prefix}}}\mspace{20mu}} \\{- 6} & {{{{{for}\mspace{14mu} p} \in \{ {17,18} \}},{{normal}\mspace{14mu}{cyclic}\mspace{14mu}{prefix}}}\mspace{20mu}} \\{- 1} & {{{{{for}\mspace{14mu} p} \in \{ {19,20} \}},{{normal}\mspace{14mu}{cyclic}\mspace{14mu}{prefix}}}\mspace{20mu}} \\{- 7} & {{{{{for}\mspace{14mu} p} \in \{ {21,22} \}},{{normal}\mspace{14mu}{cyclic}\mspace{14mu}{prefix}}}\mspace{20mu}} \\{- 0} & {{{{for}\mspace{14mu} p} \in \{ {15,16} \}},{{extended}\mspace{14mu}{cyclic}\mspace{14mu}{prefix}}} \\{- 3} & {{{{for}\mspace{14mu} p} \in \{ {17,18} \}},{{extended}\mspace{14mu}{cyclic}\mspace{14mu}{prefix}}} \\{- 6} & {{{{for}\mspace{14mu} p} \in \{ {19,20} \}},{{extended}\mspace{14mu}{cyclic}\mspace{14mu}{prefix}}} \\{- 9} & {{{{for}\mspace{14mu} p} \in \{ {21,22} \}},{{extended}\mspace{14mu}{cyclic}\mspace{14mu}{prefix}}}\end{matrix}l} = {l^{\prime} + \{ {{\begin{matrix}{l^{''}\mspace{11mu}} & {{{{CSI}\mspace{14mu}{reference}\mspace{14mu}{signal}\mspace{14mu}{configurations}\mspace{14mu} 0\text{-}19},{{normal}\mspace{14mu}{cyclic}\mspace{14mu}{prefix}}}\mspace{20mu}} \\{2l^{''}} & {{{{CSI}\mspace{14mu}{reference}\mspace{14mu}{signal}\mspace{14mu}{configurations}\mspace{14mu} 20\text{-}31},{{normal}\mspace{14mu}{cyclic}\mspace{14mu}{prefix}}}\;} \\{l^{''}\mspace{11mu}} & {{{CSI}\mspace{14mu}{reference}\mspace{14mu}{signal}\mspace{14mu}{configurations}\mspace{14mu} 0\text{-}27},{{extended}\mspace{14mu}{cyclic}\mspace{14mu}{prefix}}}\end{matrix}w_{l^{''}}} = \{ {{{\begin{matrix}{1\mspace{56mu}} & {p \in \{ {15,17,19,21} \}} \\( {- 1} )^{l^{''}} & {p \in \{ {16,18,20,22} \}}\end{matrix}l^{''}} = 0},{{1m} = 0},1,\ldots\;,{{N_{RB}^{DL} - {1m^{\prime}}} = {m + \lfloor \frac{N_{RB}^{\max,{DL}} - N_{RB}^{DL}}{2} \rfloor}}} } }} }}} & \lbrack {{Equation}\mspace{14mu} 12} \rbrack\end{matrix}$

In Equation 12, (k′,l′) (wherein k′ is a subcarrier index within aresource block and l′ indicates an OFDM symbol index within a slot.) andthe condition of n_s is determined depending on a CSI-RS configuration,such as Table 3 or Table 4.

Table 3 illustrates the mapping of (k′,l′) from a CSI-RS configurationin a normal CP.

TABLE 3 CSI Number of CSI reference signals configured reference 1 or 24 8 signal n_(s) n_(s) n_(s) configu- mod mod mod ration (k′, l′) 2 (k′,l′) 2 (k′, l′) 2 Frame 0 (9, 5) 0 (9, 5) 0 (9, 5) 0 structure 1 (11, 2) 1 (11, 2)  1 (11, 2)  1 type 1 2 (9, 2) 1 (9, 2) 1 (9, 2) 1 and 2 3 (7,2) 1 (7, 2) 1 (7, 2) 1 4 (9, 5) 1 (9, 5) 1 (9, 5) 1 5 (8, 5) 0 (8, 5) 06 (10, 2)  1 (10, 2)  1 7 (8, 2) 1 (8, 2) 1 8 (6, 2) 1 (6, 2) 1 9 (8, 5)1 (8, 5) 1 10 (3, 5) 0 11 (2, 5) 0 12 (5, 2) 1 13 (4, 2) 1 14 (3, 2) 115 (2, 2) 1 16 (1, 2) 1 17 (0, 2) 1 18 (3, 5) 1 19 (2, 5) 1 Frame 20(11, 1)  1 (11, 1)  1 (11, 1)  1 structure 21 (9, 1) 1 (9, 1) 1 (9, 1) 1type 2 22 (7, 1) 1 (7, 1) 1 (7, 1) 1 only 23 (10, 1)  1 (10, 1)  1 24(8, 1) 1 (8, 1) 1 25 (6, 1) 1 (6, 1) 1 26 (5, 1) 1 27 (4, 1) 1 28 (3, 1)1 29 (2, 1) 1 30 (1, 1) 1 31 (0, 1) 1

Table 4 illustrates the mapping of (k′,l′) from a CSI-RS configurationin an extended CP.

TABLE 4 CSI Number of CSI reference signals configured reference 1 or 24 8 signal n_(s) n_(s) n_(s) configu- mod mod mod ration (k′, l′) 2 (k′,l′) 2 (k′, l′) 2 Frame 0 (11, 4)  0 (11, 4)  0 (11, 4) 0 structure 1 (9,4) 0 (9, 4) 0  (9, 4) 0 type 1 2 (10, 4)  1 (10, 4)  1 (10, 4) 1 and 2 3(9, 4) 1 (9, 4) 1  (9, 4) 1 4 (5, 4) 0 (5, 4) 0 5 (3, 4) 0 (3, 4) 0 6(4, 4) 1 (4, 4) 1 7 (3, 4) 1 (3, 4) 1 8 (8, 4) 0 9 (6, 4) 0 10 (2, 4) 011 (0, 4) 0 12 (7, 4) 1 13 (6, 4) 1 14 (1, 4) 1 15 (0, 4) 1 Frame 16(11, 1)  1 (11, 1)  1 (11, 1) 1 structure 17 (10, 1)  1 (10, 1)  1(10, 1) 1 type 2 18 (9, 1) 1 (9, 1) 1  (9, 1) 1 only 19 (5, 1) 1 (5, 1)1 20 (4, 1) 1 (4, 1) 1 21 (3, 1) 1 (3, 1) 1 22 (8, 1) 1 23 (7, 1) 1 24(6, 1) 1 25 (2, 1) 1 26 (1, 1) 1 27 (0, 1) 1

Referring to Table 3 and Table 4, in the transmission of a CSI-RS, inorder to reduce inter-cell interference (ICI) in a multi-cellenvironment including a heterogeneous network (HetNet) environment, amaximum of 32 different configurations (in the case of a normal CP) or amaximum of 28 different configurations (in the case of an extended CP)are defined.

The CSI-RS configuration is different depending on the number of antennaports and a CP within a cell, and a neighboring cell may have a maximumof different configurations. Furthermore, the CSI-RS configuration maybe divided into a case where it is applied to both an FDD frame and aTDD frame and a case where it is applied to only a TDD frame dependingon a frame structure.

(k′,l′) and n_s are determined depending on a CSI-RS configuration basedon Table 3 and Table 4, and time-frequency resources used for CSI-RStransmission are determined depending on each CSI-RS antenna port.

FIG. 8A, FIG. 8B and FIG. 8C are diagrams illustrating resources towhich reference signals are mapped in a wireless communication system towhich the present invention may be applied.

FIG. 8A shows twenty types of CSI-RS configurations available for CSI-RStransmission by one or two CSI-RS antenna ports, FIG. 8B shows ten typesof CSI-RS configurations available for four CSI-RS antenna ports, andFIG. 8C shows five types of CSI-RS configurations available for eightCSI-RS antenna ports.

As described above, radio resources (i.e., an RE pair) in which a CSI-RSis transmitted are determined depending on each CSI-RS configuration.

If one or two antenna ports are configured for CSI-RS transmission withrespect to a specific cell, the CSI-RS is transmitted on radio resourceson a configured CSI-RS configuration of the twenty types of CSI-RSconfigurations shown in FIG. 8A.

Likewise, when four antenna ports are configured for CSI-RS transmissionwith respect to a specific cell, a CSI-RS is transmitted on radioresources on a configured CSI-RS configuration of the ten types ofCSI-RS configurations shown in FIG. 8B. Furthermore, when eight antennaports are configured for CSI-RS transmission with respect to a specificcell, a CSI-RS is transmitted on radio resources on a configured CSI-RSconfiguration of the five types of CSI-RS configurations shown in FIG.8C.

A CSI-RS for each antenna port is subjected to CDM for every two antennaports (i.e., {15,16}, {17,18}, {19,20} and {21,22}) on the same radioresources and transmitted. For example, in the case of antenna ports 15and 16, CSI-RS complex symbols for the respective antenna ports 15 and16 are the same, but are multiplied by different types of orthogonalcode (e.g., Walsh code) and mapped to the same radio resources. Thecomplex symbol of the CSI-RS for the antenna port 15 is multiplied by[1, 1], and the complex symbol of the CSI-RS for the antenna port 16 ismultiplied by [1 −1] and mapped to the same radio resources. The same istrue of the antenna ports {17,18}, {19,20} and {21,22}.

A UE may detect a CSI-RS for a specific antenna port by multiplying codeby which a transmitted symbol has been multiplied. That is, atransmitted symbol is multiplied by the code [1 1] multiplied in orderto detect the CSI-RS for the antenna port 15, and a transmitted symbolis multiplied by the code [1 −1] multiplied in order to detect theCSI-RS for the antenna port 16.

Referring to FIG. 8A to FIG. 8C, in the case of the same CSI-RSconfiguration index, radio resources according to a CSI-RS configurationhaving a large number of antenna ports include radio resources having asmall number of CSI-RS antenna ports. For example, in the case of aCSI-RS configuration 0, radio resources for the number of eight antennaports include both radio resources for the number of four antenna portsand radio resources for the number of one or two antenna ports.

A plurality of CSI-RS configurations may be used in one cell. 0 or oneCSI-RS configuration may be used for a non-zero power (NZP) CSI-RS, and0 or several CSI-RS configurations may be used for a zero power (ZP)CSI-RS.

For each bit set to 1 in a zeropower (ZP) CSI-RS (‘ZeroPowerCSI-RS) thatis a bitmap of 16 bits configured by a high layer, a UE assumes zerotransmission power in REs (except a case where an RE overlaps an REassuming a NZP CSI-RS configured by a high layer) corresponding to thefour CSI-RS columns of Table 3 and Table 4. The most significant bit(MSB) corresponds to the lowest CSI-RS configuration index, and nextbits in the bitmap sequentially correspond to next CSI-RS configurationindices.

A CSI-RS is transmitted only in a downlink slot that satisfies thecondition of (n_s mod 2) in Table 3 and Table 4 and a subframe thatsatisfies the CSI-RS subframe configurations.

In the case of the frame structure type 2 (TDD), a CSI-RS is nottransmitted in a special subframe, a synchronization signal (SS), asubframe colliding against a PBCH or SystemInformationBlockType1 (SIB 1)Message transmission or a subframe configured to paging messagetransmission.

Furthermore, an RE in which a CSI-RS for any antenna port belonging toan antenna port set S (S={15}, S={15,16}, S={17,18}, S={19,20} orS={21,22}) is transmitted is not used for the transmission of a PDSCH orfor the CSI-RS transmission of another antenna port.

Time-frequency resources used for CSI-RS transmission cannot be used fordata transmission. Accordingly, data throughput is reduced as CSI-RSoverhead is increased. By considering this, a CSI-RS is not configuredto be transmitted every subframe, but is configured to be transmitted ineach transmission period corresponding to a plurality of subframes. Inthis case, CSI-RS transmission overhead can be significantly reducedcompared to a case where a CSI-RS is transmitted every subframe.

A subframe period (hereinafter referred to as a “CSI transmissionperiod”) T_CSI-RS and a subframe offset Δ_CSI-RS for CSI-RS transmissionare shown in Table 5.

Table 5 illustrates CSI-RS subframe configurations.

TABLE 5 CSI-RS- CSI-RS periodicity CSI-RS subframe offset SubframeConfigT_(CSI-RS) Δ_(CSI-RS) I_(CSI-RS) (subframes) (subframes) 0-4 5I_(CSI-RS)  5-14 10 I_(CSI-RS) − 5  15-34 20 I_(CSI-RS) − 15 35-74 40I_(CSI-RS) − 35  75-154 80 I_(CSI-RS) − 75

Referring to Table 5, the CSI-RS transmission period T_CSI-RS and thesubframe offset Δ_CSI-RS are determined depending on the CSI-RS subframeconfiguration I_CSI-RS.

The CSI-RS subframe configuration of Table 5 may be configured as one ofthe aforementioned ‘SubframeConfig’ field and‘zeroTxPowerSubframeConfig’ field. The CSI-RS subframe configuration maybe separately configured with respect to an NZP CSI-RS and a ZP CSI-RS.

A subframe including a CSI-RS satisfies Equation 13.(10n _(f) +└n _(s)/2┘−Δ_(CSI-RS))mod T _(CSI-RS)=0  [Equation 13]

In Equation 13, T_CSI-RS means a CSI-RS transmission period, Δ_CSI-RSmeans a subframe offset value, n_f means a system frame number, and n_smeans a slot number.

In the case of a UE in which the transmission mode 9 has been configuredwith respect to a serving cell, one CSI-RS resource configuration may beconfigured for the UE. In the case of a UE in which the transmissionmode 10 has been configured with respect to a serving cell, one or moreCSI-RS resource configuration (s) may be configured for the UE.

In the current LTE standard, a CSI-RS configuration includes an antennaport number (antennaPortsCount), a subframe configuration(subframeConfig), and a resource configuration (resourceConfig).Accordingly, the a CSI-RS configuration provides notification that aCSI-RS is transmitted how many antenna port, provides notification ofthe period and offset of a subframe in which a CSI-RS will betransmitted, and provides notification that a CSI-RS is transmitted inwhich RE location (i.e., a frequency and OFDM symbol index) in acorresponding subframe.

Specifically, the following parameters for each CSI-RS (resource)configuration are configured through high layer signaling.

-   -   If the transmission mode 10 has been configured, a CSI-RS        resource configuration identifier    -   A CSI-RS port number (antennaPortsCount): a parameter (e.g., one        CSI-RS port, two CSI-RS ports, four CSI-RS ports or eight CSI-RS        ports) indicative of the number of antenna ports used for CSI-RS        transmission    -   A CSI-RS configuration (resourceConfig) (refer to Table 3 and        Table 4): a parameter regarding a CSI-RS allocation resource        location    -   A CSI-RS subframe configuration (subframeConfig, that is,        I_CSI-RS) (refer to Table 5): a parameter regarding the period        and/or offset of a subframe in which a CSI-RS will be        transmitted    -   If the transmission mode 9 has been configured, transmission        power P_C for CSI feedback: in relation to the assumption of a        UE for reference PDSCH transmission power for feedback, when the        UE derives CSI feedback and takes a value within a [−8, 15] dB        range in a 1-dB step size, P_C is assumed to be the ratio of        energy per resource element (EPRE) per PDSCH RE and a CSI-RS        EPRE.    -   If the transmission mode 10 has been configured, transmission        power P_C for CSI feedback with respect to each CSI process. If        CSI subframe sets C_CSI,0 and C_CSI,1 are configured by a high        layer with respect to a CSI process, P_C is configured for each        CSI subframe set in the CSI process.    -   A pseudo-random sequence generator parameter n_ID    -   If the transmission mode 10 has been configured, a high layer        parameter ‘qcl-CRS-Info-r11’ including a QCL scrambling        identifier for a quasico-located (QCL) type B UE assumption        (qcl-ScramblingIdentity-r11), a CRS port count        (crs-PortsCount-r11), and an MBSFN subframe configuration list        (mbsfn-SubframeConfigList-r11) parameter.

When a CSI feedback value derived by a UE has a value within the [−8,15] dB range, P_C is assumed to be the ration of PDSCH EPRE to CSI-RSEPRE. In this case, the PDSCH EPRE corresponds to a symbol in which theratio of PDSCH EPRE to CRS EPRE is p_A.

A CSI-RS and a PMCH are not configured in the same subframe of a servingcell at the same time.

In the frame structure type 2, if four CRS antenna ports have beenconfigured, a CSI-RS configuration index belonging to the [20-31] set(refer to Table 3) in the case of a normal CP or a CSI-RS configurationindex belonging to the [16-27] set (refer to Table 4) in the case of anextended CP is not configured in a UE.

A UE may assume that the CSI-RS antenna port of a CSI-RS resourceconfiguration has a QCL relation with delay spread, Doppler spread,Doppler shift, an average gain and average delay.

A UE in which the transmission mode 10 and the QCL type B have beenconfigured may assume that antenna ports 0-3 corresponding to a CSI-RSresource configuration and antenna ports 15-22 corresponding to a CSI-RSresource configuration have QCL relation with Doppler spread and Dopplershift.

In the case of a UE in which the transmission modes 1-9 have beenconfigured, one ZP CSI-RS resource configuration may be configured inthe UE with respect to a serving cell. In the case of a UE in which thetransmission mode 10 has been configured, one or more ZP CSI-RS resourceconfigurations may be configured in the UE with respect to a servingcell.

The following parameters for a ZP CSI-RS resource configuration may beconfigured through high layer signaling.

The ZP CSI-RS configuration list (zeroTxPowerResourceConfigList) (referto Table 3 and Table 4): a parameter regarding a zero-power CSI-RSconfiguration

The ZP CSI-RS subframe configuration (eroTxPowerSubframeConfig, that is,I_CSI-RS) (refer to Table 5): a parameter regarding the period and/oroffset of a subframe in which a zero-power CSI-RS is transmitted

A ZP CSI-RS and a PMCH are not configured in the same subframe of aserving cell at the same time.

In the case of a UE in which the transmission mode 10 has beenconfigured, one or more channel state information—interferencemeasurement (CSI-IM) resource configurations may be configured in the UEwith respect to a serving cell.

The following parameters for each CSI-IM resource configuration may beconfigured through high layer signaling.

-   -   The ZP CSI-RS configuration (refer to Table 3 and Table 4)    -   The ZP CSI RS subframe configuration I_CSI-RS (refer to Table 5)

A CSI-IM resource configuration is the same as any one of configured ZPCSI-RS resource configurations.

A CSI-IM resource and a PMCH are not configured within the same subframeof a serving cell at the same time.

Sounding Reference Signal (SRS)

An SRS is mainly used for channel quality measurement to perform uplinkfrequency-selective scheduling and is not related to transmission ofuplink data and/or control information. However, the present inventionis not limited thereto and the SRS may be used for various otherpurposes to enhance power control or to support various start-upfunctions of recently unscheduled terminals. As an example of thestart-up function, an initial modulation and coding scheme (MCS),initial power control for data transmission, timing advance, andfrequency semi-selective scheduling may be included. In this case,frequency semi-selective scheduling refers to scheduling thatselectively allocates frequency resources to a first slot of a subframeand allocating the frequency resources by pseudo-randomly jumping toanother frequency in a second slot.

Further, the SRS may be used for measuring a downlink channel qualityunder the assumption that radio channels are reciprocal between theuplink and the downlink. The assumption is particularly effective in atime division duplex (TDD) system in which the uplink and the downlinkshare the same frequency spectrum and are separated in a time domain.

The SRS subframes transmitted by a certain UE in a cell may berepresented by a cell-specific broadcast signal. A 4 bit cell-specific‘srsSubframeConfiguration’ parameter represents 15 available subframearrays through which the SRS may be transmitted over each radio frame.The arrays provide flexibility for adjustment of SRS overhead accordingto a deployment scenario.

A 16-th array completely turns off a switch of the SRS in the cell andthis is primarily suitable for a serving cell that serves high-speedterminals.

FIG. 9 illustrates an uplink subframe including a sounding referencesignal symbol in a wireless communication system to which the presentinvention may be applied.

Referring to FIG. 9, the SRS is continuously transmitted on the lastSC-FDMA symbol on the arranged subframe. Therefore, the SRS and the DMRSare located in different SC-FDMA symbols.

PUSCH data transmission is not allowed in a specific SC-FDMA symbol forSRS transmission and as a result, when the sounding overhead is thehighest, that is, even if SRS symbols are included in all subframes, thesounding overhead does not exceed approximately 7%.

Each SRS symbol is generated by a basic sequence (random sequence or asequence set based on Zadoff-Ch (ZC)) for a given time unit andfrequency band, and all terminals in the same cell use the same basicsequence. In this case, the SRS transmissions from a plurality of UEs inthe same cell at the same time in the same frequency band are orthogonalby different cyclic shifts of the basic sequence, and are distinguishedfrom each other.

By assigning different basic sequences to respective cells, the SRSsequences from different cells may be distinguished, but orthogonalitybetween different basic sequences is not guaranteed.

As more and more communication devices require larger communicationcapacity, there is a need for improved mobile broadband communicationcompared to the existing radio access technology (RAT). Massive machinetype communications (MTCs), which provide various services anytime andanywhere by connecting many devices and objects, are one of the majorissues to be considered in the next generation communication. Inaddition, a communication system design considering a service/UEsensitive to reliability and latency is being discussed.

The introduction of next generation radio access technology consideringenhanced mobile broadband communication, massive MTC, ultra-reliable andlow latency communication (URLLC) is discussed, and in the presentinvention, the technology is called new RAT for convenience.

Self-Contained Subframe Structure

FIG. 10 is a diagram illustrating a self-contained subframe structure inthe wireless communication system to which the present invention may beapplied.

In a TDD system, in order to minimize the latency of data transmission,a 5 generation (5G) new RAT considers a self-contained subframestructure as shown in FIG. 10.

In FIG. 10, a dashed area (symbol index of 0) indicates a downlink (DL)control area and a black area (symbol index of 13) indicates an uplink(UL) control area. An unmarked area may also be used for DL datatransmission or for UL data transmission. Such a structure ischaracterized in that DL transmission and UL transmission aresequentially performed in one subframe, and DL data is transmitted in asubframe, and UL ACK/NACK may also be received. As a result, it takesless time to retransmit data when a data transmission error occurs,thereby minimizing the latency of final data transmission.

In such a self-contained subframe structure, there is a need for a timegap between the base station and the UE for the conversion process fromthe transmission mode to the reception mode or from the reception modeto the transmission mode. For this end, some OFDM symbols at the time ofswitching from DL to UL in the self-contained subframe structure areconfigured to a guard period (GP).

Analog Beamforming

In a millimeter wave (mmW), a wavelength is shortened, so that aplurality of antenna elements may be installed in the same area. Thatis, a total of 64 (8×8) antenna elements may be installed in a2-dimension array at a 0.5 lambda (that is, wavelength) interval on apanel of 4×4 (4 by 4) cm with a wavelength of 1 cm in a 30 GHz band.Therefore, in the mmW, it is possible to increase a beamforming (BF)gain to increase coverage or increase throughput by using multipleantenna elements.

In this case, if a transceiver unit (TXRU) is provided so thattransmission power and phase may be adjusted for each antenna element,independent beamforming is possible for each frequency resource.However, when the TXRUs are installed on all 100 antenna elements, thereis a problem that effectiveness is deteriorated in terms of costs.Therefore, a method of mapping a plurality of antenna elements to oneTXRU and adjusting a direction of a beam using an analog phase shifteris considered. Such an analog BF method has a disadvantage in thatfrequency selective BF may not be performed by making only one beamdirection in all bands.

A hybrid BF with B TXRUs, which is an intermediate form of digital BFand analog BF, and fewer than Q antenna elements, may be considered. Inthis case, although there is a difference depending on a connectionmethod of B TXRUs and Q antenna elements, the number of directions ofthe beams that may be transmitted at the same time is limited to B orless.

Hereinafter, representative examples of a method of connection method ofTXRUs and antenna elements will be described with reference to theaccompanying drawing.

FIG. 11A and FIG. 11B show a transceiver unit model in a radiocommunication system to which the present invention may be applied.

A TXRU virtualization model shows a relationship between an outputsignal of the TXRUs and an output signal of the antenna elements.According to the correlation between the antenna element and the TXRU,The TXRU virtualization model may be divided into TXRU virtualizationmodel option-1 and a sub-array partition model as illustrated in FIG.11A and TXRU virtualization model option-2 and a full-connection modelas illustrated in FIG. 11B.

Referring to FIG. 11A, in the case of the sub-array partition model, theantenna element is divided into multiple antenna element groups and eachTXRU is connected to one of the groups. In this case, the antennaelement is connected to only one TXRU.

Referring to FIG. 11B, in the case of the full-connection model, signalsof multiple TXRUs are combined and transmitted to a single antennaelement (or an array of antenna elements). That is, a scheme isillustrated, in which the TXRU is connected to all antenna elements. Inthis case, the antenna element is connected to all TXRUs.

In FIG. 11A and FIG. 11B, q represents a transmission signal vector ofantenna elements having M co-polarized waves in one column. w representsa wideband TXRU virtualization weight vector and W represents a phasevector multiplied by an analog phase shifter. In other words, thedirection of analog beamforming is determined by W. x represents asignal vector of M_TXRU TXRUs.

Herein, mapping of the antenna ports and the TXRUs may be 1-to-1 or1-to-many.

In FIG. 11A and FIG. 11B, the mapping (TXRU-to-element mapping) betweenthe TXRU and the antenna element is merely an example, and the presentinvention is not limited thereto. The present invention may be similarlyapplied even to mapping between the TXRU and the antenna element, whichmay be implemented in various other forms in terms of hardware.

Feedback of Channel State Information (CSI)

In a 3GPP LTE/LTE-A system, user equipment (UE) is defined to reportchannel state information (CSI) to a base station (BS or eNB).

The CSI collectively refers to information that may indicate the qualityof a radio channel (or referred to as a link) formed between the UE andthe antenna port. For example, a rank indicator (RI), a precoding matrixindicator (PMI), a channel quality indicator (CQI), and the likecorrespond to the information.

Here, the RI represents rank information of a channel, which means thenumber of streams received by the UE through the same time-frequencyresource. Since this value is determined depending on the long termfading of the channel, the value is fed back from the UE to the BS witha period usually longer than the PMI and the CQI. The PMI is a valuereflecting a channel space characteristic and represents a preferredprecoding index preferred by the UE based on a metric such assignal-to-interference-plus-noise ratio (SINR). The CQI is a valuerepresenting the strength of the channel, and generally refers to areception SINR that may be obtained when the BS uses the PMI.

In the 3GPP LTE/LTE-A system, the BS configures a plurality of CSIprocesses to the UE and may receive CSI for each process. Here, the CSIprocess is constituted by a CSI-RS for signal quality measurement fromthe BS and a CSI-interference measurement (CSI-IM) resource forinterference measurement.

Reference Signal (RS) Virtualization

In the mmW, it is possible to transmit a PDSCH only in one analog beamdirection at a time by analog beamforming. In this case, datatransmission from the BS is possible only to a small number of UEs inthe corresponding direction. Therefore, if necessary, the analog beamdirection is differently configured for each antenna port so that datatransmission may be simultaneously performed to a plurality of UEs inseveral analog beam directions.

FIG. 12A, FIG. 12B and FIG. 12C are diagrams illustrating a service areafor each transceiver unit in the wireless communication system to whichthe present invention may be applied.

In FIG. 12A to FIG. 12C, 256 antenna elements are divided into 4 partsto form a 4 sub-arrays, and the structure of connecting the TXRU to thesub-array will be described as an example as shown in FIG. 11A and FIG.11B above.

When each sub-array is constituted by a total of 64 (8×8) antennaelements in the form of a 2-dimensional array, specific analogbeamforming may cover an area corresponding to a 15-degree horizontalangle area and a 15-degree vertical angle area. That is, the zone wherethe BS should be served is divided into a plurality of areas, andservices are provided one by one at a time.

In the following description, it is assumed that the CSI-RS antennaports and the TXRUs are 1-to-1 mapped. Therefore, the antenna port andthe TXRU have the same meaning as the following description.

As shown in FIG. 12A, if all TXRUs (antenna ports, sub-arrays) (that is,TXRU 0, 1, 2, 3) have the same analog beamforming direction (that is,region 1), the throughput of the corresponding zone may be increased byforming digital beam with higher resolution. Also, it is possible toincrease the throughput of the corresponding zone by increasing the rankof the transmission data to the corresponding zone.

As shown in FIG. 12B and FIG. 12C, if each TXRU (antenna port,sub-array) (that is, TXRU 0, 1, 2, 3) has a different analog beamformingdirection (that is, region 1 or region 2, the data may be transmittedsimultaneously to UEs distributed in a wider area in the subframe (SF).

As an example shown in FIGS. 12(b) and 12(c), two of the four antennaports are used for PDSCH transmission to UE1 in region 1 and theremaining two antenna ports are used for PDSCH transmission to UE2 inregion 2.

Particularly, in FIG. 12B, PDSCH1 transmitted to UE1 and PDSCH2transmitted to UE2 represent examples of spatial division multiplexing(SDM). Unlike this, as shown in FIG. 12C, PDSCH1 transmitted to UE1 andPDSCH2 transmitted to UE2 may also be transmitted by frequency divisionmultiplexing (FDM).

Among a scheme of serving one area using all the antenna ports and ascheme of serving many areas at the same time by dividing the antennaports, a preferred scheme is changed according to the rank and themodulation and coding scheme (MCS) servicing to the UE for maximizingthe cell throughput. Also, the preferred method is changed according tothe amount of data to be transmitted to each UE.

The BS calculates a cell throughput or scheduling metric which may beobtained when one area is served using all the antenna ports, andcalculates the cell throughput or scheduling metric which may beobtained when two areas are served by dividing the antenna ports. The BScompares the cell throughput or the scheduling metric which may beobtained by each scheme to select the final transmission scheme. As aresult, the number of antenna ports participating in PDSCH transmissionis changed by SF-by-SF. In order for the BS to calculate thetransmission MCS of the PDSCH according to the number of antenna portsand reflect the calculated transmission MCS to a scheduling algorithm,the CSI feedback from the appropriate UE is required.

Beam Reference Signal (BRS)

Beam reference signals are transmitted on one or more antenna ports(p={0, 1, . . . , 7}).

The reference-signal sequence ‘r_l(m)’ may be defined by Equation 14below.

$\begin{matrix}{{{r_{l}(m)} = {{\frac{1}{\sqrt{2}}( {1 - {2 \cdot {c( {2m} )}}} )} + {j\frac{1}{\sqrt{2}}( {1 - {2 \cdot {c( {{2m} + 1} )}}} )}}},{m = 0},1,\ldots\;,{{8 \cdot ( {N_{RB}^{\max,{DL}} - 18} )} - 1}} & \lbrack {{Equation}\mspace{14mu} 14} \rbrack\end{matrix}$

Where I=0, 1, . . . , 13 is the OFDM symbol number. N_RB{circumflex over( )}max,DL represents the largest downlink band configuration andN_sc{circumflex over ( )}RB is expressed by a multiple. N_sc{circumflexover ( )}RB represents the size of the resource block in the frequencydomain and is expressed by the number of subcarriers.

In Equation 14, c(i) may be predefined as a pseudo-random sequence. Thepseudo-random sequence generator may be initialized at the start of eachOFDM symbol by using Equation 15 below.C _(init)=2¹⁰·(7·(n _(s)+1)+l′+1)·(2·N _(ID) ^(cell)+1)+2·N _(ID)^(cell)+1  [Equation 15]

Where N_ID{circumflex over ( )}cell represents a physical layer cellidentifier. n_s=floor(l/7) and floor(x) represents a floor function forderiving a maximum integer of x or less. l′=l mod 7 and mod represents amodulo operation.

Beam Refinement Reference Signal (BRRS)

Beam refinement reference signals (BRRSs) may be transmitted on up toeight antenna ports (p=600, . . . , 607). The transmission and receptionof the BRRS are dynamically scheduled in the downlink resourceallocation on xPDCCH.

The reference-signal sequence ‘r_l,ns(m)’ may be defined by Equation 16below.

$\begin{matrix}{{{r_{l,n_{s}}(m)} = {{\frac{1}{\sqrt{2}}( {1 - {2{c( {2m} )}}} )} + {j\frac{1}{\sqrt{2}}( {1 - {2{c( {{2m} + 1} )}}} )}}},{m = 0},1,\ldots\;,{\lfloor {\frac{3}{8}N_{RB}^{\max,{DL}}} \rfloor - 1}} & \lbrack {{Equation}\mspace{14mu} 16} \rbrack\end{matrix}$

Where n_s represents the slot number in the radio frame. I representsthe OFDM symbol number in the slot. c(i) may be predefined as thepseudo-random sequence. The pseudo-random sequence generator may beinitialized at the start of each OFDM symbol by using Equation 17 below.c _(init)=2¹⁰(7( n _(s)+1)+l+1)(2N _(ID) ^(BRRS)+1)+2N _(ID) ^(BRRS)+1n _(s) =n _(s)mod 20  [Equation 17]

Herein, N_ID{circumflex over ( )}BRRS is configured to the UE throughthe RRC signaling.

DL Phase Noise Compensation Reference Signal

Phase noise compensation reference signals associated with xPDSCH may betransmitted on antenna port(s) p=60 and/or p=61 according to thesignaling in the DCI. Further, the phase noise compensation referencesignals associated with xPDSCH may be present as a valid reference forphase noise compensation only if the xPDSCH transmission is associatedwith the corresponding antenna port. In addition, the phase noisecompensation reference signals associated with xPDSCH may be transmittedonly on the physical resource blocks and symbols upon which thecorresponding xPDSCH is mapped. Moreover, the phase noise compensationreference signals associated with xPDSCH may be identical in all symbolswith xPDSCH allocation.

For any antenna port p∈{60,61}, the reference-signal sequence ‘r(m)’ isdefined by Equation 18 below.

$\begin{matrix}{{{r(m)} = {{\frac{1}{\sqrt{2}}( {1 - {2 \cdot {c( {2m} )}}} )} + {j\frac{1}{\sqrt{2}}( {1 - {2 \cdot {c( {{2m} + 1} )}}} )}}},{m = 0},1,\ldots\;,{\lfloor {N_{RB}^{\max,{DL}}\text{/}4} \rfloor - 1}} & \lbrack {{Equation}\mspace{14mu} 18} \rbrack\end{matrix}$

Herein, c(i) may be predefined as the pseudo-random sequence. Thepseudo-random sequence generator may be initialized at the start of eachsubframe by using Equation 19 below.c _(init)=(└n _(s)/2┘+1)·(2n _(ID) ^((n) ^(SCID) ⁾+1)·2¹⁶ +n_(SCID[Equation) 19]

Where n_SCID is 0 if unless specified otherwise. In the xPDSCHtransmission, n_SCID is given in a DCI format associated with the xPDSCHtransmission.

n_ID{circumflex over ( )}(i) (where i=0, 1) is given as follows. Whenthe value of n_ID{circumflex over ( )}PCRS,i is not provided by thehigher layer, n_ID{circumflex over ( )}(i) is equal to N_ID{circumflexover ( )}cell. If not, n_ID{circumflex over ( )}(i) is equal ton_ID{circumflex over ( )}PCRS,i.

The following techniques are discussed for new RAT (NR) uplink (UL)multi-input multi-output (MIMO).

i) Uplink transmission/reception schemes for data channels

-   -   Non reciprocity based UL MIMO (e.g., PMI based)    -   Reciprocity based UL MIMO (e.g., UE derives precoder based on        downlink RS measurement (including partial reciprocity)    -   Support of multi user (MU)-MIMO    -   Open-loop/Close-loop single/Multi point spatial multiplexing        (SM)

For example, for multi point SM, multi layers are received eitherjointly or independently by different transmit reception points (TRPs).

For multi point SM, multiple points may be coordinated.

-   -   Single/Multi panel spatial diversity    -   Uplink antenna/panel switching (UE side)    -   UL beamforming management for analog implementation    -   Combination of above techniques

ii) UL RS design considering the below functions

-   -   Sounding    -   Demodulation    -   Phase noise compensation

iii) UL transmit power/timing advance control in the context of UL MIMO

iv) Transmission scheme(s) for carrying UL control information

v) Other UL MIMO and related techniques are not limited.

The following aspects for UL MIMO transmission should be supported:

i) Transmission schemes/methods for reciprocity calibrated UEs,reciprocity non-calibrated UEs, and non-reciprocity/partial reciprocitycases

-   -   If needed, signaling associated with UL reciprocity based        operation is introduced. For example, UE capability which        indicates calibration accuracy    -   Whether to differentiate reciprocity non-calibrated UEs from        non-reciprocity or not is to be discussed.    -   The number of transmission schemes/methods may be further        discussed.

ii) At least one of the following candidate schemes/methods is to besupported.

Candidate 1: Codebook Based Transmission

Frequency selective and frequency non-selective precoding in digitaldomain may be considered for a widesystem bandwidth. The support for thefrequency selective precoding is determined according to decision on NRwaveform(s). The value of the wide system bandwidth will be discussedlater.

For example, base station (BS)-based which is analogous to the LTE

For example, UE-aided and BS-centric mechanism: The UE recommendscandidate UL precoders from a predefined codebook to BS based on DL RSmeasurement. In addition, the BS determines the final precoder takenfrom the codebook.

For example, UE-centric and BS-aided mechanism: The BS provides CSI(e.g. channel response, interference-related information) to the UE. Inaddition, the UE determines the final precoder based on the informationfrom the BS.

Candidate 1: Non-Codebook Based Transmission

Frequency selective and frequency non-selective precoding in digitaldomain may be considered for the wide system bandwidth. The support forthe frequency selective precoding is determined according to decision onNR waveform(s). The value of the wide system bandwidth will be discussedlater.

For example, reciprocity based (DL RS based) transmission only forcalibrated UEs

For example, UE-aided and BS-centric mechanism: The UE recommendscandidate UL precoders to the BS based on DL RS measurement. Inaddition, the BS determines the final precoder.

For example, UE-centric and BS-aided mechanism: The BS provides CSI(e.g. channel response, interference-related information) to the UE. Inaddition, the UE determines the final precoder based on the informationfrom the BS.

Other transmission schemes/methods are not limited.

i) Discussion of UL precoder signaling for frequencyselective/non-selective precoding

Example 1: Signaling of Single or Multiple PMIs Via DL Control and/orData Channels

Multiple PMIs may be signaled via a single DCI or multi-level DCI(1^(st) level DCI contains a location indication to the 2^(nd) levelDCI).

Example 2: For TDD, Precoder Calculation at the UE Based on DL RS

The implementation of the frequency selective precoding is determinedaccording to RAN1 decision (e.g. NR frame structure, waveform(s)).

An influence on other system design aspects (e.g. DL control channeldecoding performance/complexity) should be considered.

ii) Discussion of the use of UL frequency selective precoding forprecoded transmission including precoder cycling

iii) For frequency selective precoding, discussion of UL precodinggranularity (i.e. UL subband size) considering following aspects

-   -   Implicit (defined by spec.) or explicit (by eNB/UE decision)        signaling support    -   Whether to align with DL

iv) Evaluation should include UL specific aspects such as cubic metric(CM) analysis according to UL waveform, etc.

v) Discussion of frequency non-selective precoding is ofhigher-priority.

In the existing LTE standard, when a base station transmits an uplink(UL) grant for UL-MIMO transmission of a UE (e.g., by DCI format 4) tothe UE, the base station transmits precoding information (e.g., includedin the DCI format) together. Accordingly, the UE performs ULtransmission by applying the indicated (single wideband) precoder toscheduled physical resource block(s) (PRB(s)).

As described above, a method for instructing a frequency selectiveprecoder even in the UL is also considered. As a result, it is possibleto improve the transmission yield performance by applying a moreoptimized UL precoder for each subband.

However, unlike the DL, the UL needs to directly instruct the subbandprecoder at the time of UL grant of the base station, which may cause anexcessive control channel overhead in proportion to the number ofsubbands.

Therefore, the present invention proposes schemes for applying the ULsubband precoding while minimizing the UL-related DCI overhead.

In the present invention, a specific UL precoder ‘P’ is basicallydescribed to be divided into a type of P=U1*U2 and the like. Here, itmay be divided into U1 as a relative wideband (and/or long-term)precoder attribute and U2 as a relative subband (and/or short-term)precoder attribute.

However, the present invention is not limited thereto, and the operationof the present invention to be described below may be performed based asingle PMI (e.g., TPMI) and a precoder.

There is provided a method in which UI information is indicated to becommon throughout the subbands and only U2 information is indicated foreach subband to be instructed to the UE at the time of UL scheduling (orin association with the UL scheduling).

For example, assuming that a complete P is 6 bits, U1 is 4 bits, and U2is 2 bits, 6 bits are allocated for each subband without applying ahierarchical structure proposed in the present invention. If the totalnumber is N, a total of 6N bits is consumed in the corresponding ULprecoder instruction. On the other hand, according to the proposedmethod of the present invention, since 6+2N bits are consumed, thenumber of subbands N increases, thereby contributing to reduction of acontrol channel overhead.

In this specification, for convenience of the description, a specificfrequency axis resource unit is referred to as the “subband”, but thepresent invention is not limited thereto, and it should be understoodthat the “subband” is commonly referred to as the specific frequencyaxis resource unit. For example, the term of subband may bechanged/mixed with each other in all/some description of the presentinvention, such as RB, PRB, PRB group (e.g., PRG (PRB Group)).

U1 Information Relation

For an environment (e.g., similar to an open-loop method, a case where aterminal speed is high, etc.) in which it is advantageous to selectivelyinstruct widely-spaced beams for each subband, rather than anenvironment in which it is advantageous to selectively instructclosely-spaced beam for each subband due to channel characteristics, aU1 codebook may also be configured as a widely-spaced beam.

In the above described example, 4 bits of U1 means that a total of 16different U1 information may be indicated. Each U1 information mayinclude specific beam vectors to be selected in the U2. As an example,each U1 may be constituted by a set of discrete fourier transform (DFT)vectors as many as the number of UL transmission antenna ports of the UE(e.g., the number of the ports may be transmitted in advance by the UEin a SRS form).

In this case, each U1 index may be designed in the form of aclosely-spaced beam group. As a result, it is advantageous that the basestation instructs UL scheduling by configuring the UI by peripheralcandidate beam vectors including a final specific beam direction whichintends to instruct the corresponding UE at the time of the ULscheduling. That is, since U1 is the relative wideband (and/orlong-term) precoder attribute, it is advantageous that the beams toselect/instruct the final beam optimized for each subband are stored inU1, and each U1 information should be designed so that such an effectmay be appropriately exhibited.

In the present invention, it is possible to define/configure at leastone different codebook such as a “closely-spaced beam group”, a“widely-spaced beam group”, and/or a “beam group composed of a specificform (e.g., eNB-configurable). In addition, the base station mayconfigure/instruct which U1 and/or U2 codebook the UE needs to apply atthe time of the UL scheduling (e.g., by DCI) or separate signalingbefore the UL scheduling. As a result, although such a U1 codebookitself may be fixed as one, like the present invention, there is anadvantage that a more flexible codebook may be operated by supporting afunction of changing/activating/re-activating by configuring/instructingthe base station.

U2 Information Relation

In the above described example, 2 bits of U1 means that a total of 4different U2 information may be indicated. Each U2 information may beconfigured in a form in which a beam group corresponding to the aboveindicated U1 index may include four specific beam vectors and the 2-bitU2 selection index indicates which beam among the beams is to be finallyapplied for each subband.

In addition, in the example described above, when UI is 4 bits, U2 mayexceed 2 bits. For example, if U2 is 4 bits, 2 bits are allocated as a“beam selector” so that total four different pieces of U2 informationmay be indicated. In order to connect the corresponding beam in the formof co-phasing (e.g., QPSK (Quadrature Phase Shift Keying)“co-phasing”)), 2 bits may be allocated and thus the total U2 may beconfigured as 4 bits. The co-phasing is configured in the form ofcross-polarized antennas between the specific (two) transmission antennaport groups of the UE and the same beam may be applied so as toconfigure a precoder in the form of co-phasing by applying a group-phasebetween the same groups of ports.

Alternatively, it is apparent that “co-phasing” may allocate only 1 bitto apply, for example, BPSK co-phasing and the bit width of the “beamselector” may be modified/changed according to the transmission antennaport configuration of the UE and the U1/U2 codebook structure.

The U2 information is mapped/indicated for each subband, and may beconfigured/indicated together by interlocking with the UL resourceallocation (RA) field scheduled for the corresponding UE.

For example, if resource allocation information of the corresponding ULgrant message is in the form of a specific PRB bitmap (e.g., if each bitis ‘1’, the corresponding PRB is included in the scheduled PRB and ifeach bit is ‘0’, the corresponding PRB is not included), the structuremay extend so as to store K-bit information for each PRB index withoutusing a bitmap of ‘1’ or ‘0’. That is, the information may correspond toone PRB for each K bit in the bit map. As such, in one embodiment of thepresent invention, there is proposed a structure to transmit the U2information through the corresponding 2{circumflex over ( )}K state foreach PRB.

For example, if K=2, a specific default state may be defined/configuredfor each PRB as follows.

-   -   ‘00’ indicates that “the corresponding PRB is not included in        the scheduled PRB”    -   ‘01’ indicates that “the corresponding PRB is included in the        scheduled PRB and the first precoder in U1 is applied”    -   ‘10’ indicates that “the corresponding PRB is included in the        scheduled PRB and the second precoder in U1 is applied”    -   ‘11’ indicates that “the corresponding PRB is included in the        scheduled PRB and the third precoder in U1 is applied”

Such an encoding method is just an example, and the description of thestate such as ‘01’, ‘10’, and ‘11’ may be defined in a different form orthe base station may be changed/configured by a higher layer signal suchas RRC signaling. As described above, when the description of the stateis defined/supported in the form of parameters configurable by the basestain (e.g., by RRC signaling), it is advantageous that theconfiguration flexibility of the base station may be increased.

As such, as the scheduling information and the U2 information arejointly encoded in one bitmap, it is possible to reduce the signalingoverhead compared with the case of configuring a bitmap for transmittingthe scheduling information and a bitmap for transmitting the U2information, respectively.

In addition, the RA field is maintained as a 1-bit unit bitmap, and maybe applied even in the form that a bitmap in units of K-bits fortransmitting the U2 information per subband (per PRB/PRG) is provided asa separate field (or provided separately (at an independent time) as aseparate DCI). That is, a separate field indicating K-bit (U2) precoderinformation for each subband corresponding to a specific PRB(s) in thescheduled PRB area indicated in the RA field may be defined/configured.

Operation Relation Associated with Specific Uplink Reference Signal (ULRS) (e.g., SRS) (for Link Adaptation (LA)

-   -   In association with some of the operations proposed in the        present invention, a specific RS (e.g., SRS) transmission may be        configured/implemented by the UE in order to determine the UL        precoder at the base station.

Hereinafter, for convenience of description, the uplink RS is referredto as SRS, but the present invention is not limited thereto.

1) Type 1 UL-LA UE (UL-LA process operation by starting Precoded SRStransmission):

Such a SRS may be first defined/configured to transmit a specificPrecoded SRS. In this case, the base station measures the precoded SRSof the specific port(s) to determine the proposed U1 and/or U2information. Thereafter, the base station transmits a UL schedulinggrant (e.g., in case of U1, may be separately transmitted to the UE viaa separate DCI (field) or a separate message container for specificcontrol information delivery (by L1 and/or L2 signaling) including thedetermined U1 and/or U2 information. Accordingly, there is disclosedfrequency-selective UL-MIMO scheduling considered in the presentinvention.

A type in which a UL link adaptation (UL-LA) process is initiated bystarting the precoded SRS transmission without (that is, omitting) thetransmission procedure of the specific non-precoded SRS may be referredto as a Type 1 UL-LA operation (or UE).

That is, the UE may transmit precoded/beamformed SRS ports applying, forexample, analog beamforming in a specific direction through thecorresponding specific precoded SRS. In addition, the base stationmeasures the (analog-) beamformed SRS ports to derive appropriate U1and/or U2 and then informs the derived U1 and/or U2 to the UE by themethod described above to apply the UL transmission.

More specifically, the corresponding beamforming vectors/coefficients tobe applied to the precoded/beamformed SRS by the UE may be determined asfollows. First, the UE may measure a DL specific RS (e.g., radioresource management-RS (RRM-RS), BRS, BRRS, etc.) transmitted by thebase station. In addition, the UE finds (and also reports) the best“serving-beam” to determine (paired) best “Rx-receiving-beam” of the UEitself. Then, the UE may transmit the SRS by applying the correspondingbeamforming vectors/coefficients, when transmitting theprecoded/beamformed SRS, by inverting (e.g., taking Hermitian) the best“Rx-receiving-beam” using the DUUL channel reciprocity characteristic.That is, the SRS transmission may be performed with the same spatialfiltering as the spatial filtering used for the reception of a specificDL RS (e.g., the best “serving-beam”). The operation of the UE may bedefined in advance or configured in the UE.

Alternatively, it is not necessarily limited to applying only the“Rx-receiving-beam” corresponding to the best “serving-beam”. Forexample, the operation may be supported such that the base station mayinstruct/trigger precoded/beamformed SRS transmissions applying the“Rx-receiving-beam” corresponding to the second-best “serving-beam”.

Such a method is generalized, and thus, in the same manner ascorresponding to a third-best “serving-beam”, corresponding to afourth-best “serving-beam”, . . . , a specific identifier (e.g., beamstate information (BSI), etc.) may be instructed from the base stationso as to recognize the corresponding n-th “serving-beam”. In such asform, the beamforming vectors/coefficients to be applied by the UE, whentransmitting the precoded/beamformed SRS, may be configured/indicated.

In other words, the UE may transmit the beamforming vectors/coefficientsusing the same spatial filtering as the spatial filtering used forreception of the specific DL RS when transmitting the SRS. That is, theUE may implement spatial filtering that is optimal for DL RS receptionfor each DL RS, and the base station may instruct the UE to performtransmission of a specific SRS resource using the same spatial filteringas the spatial filtering used by the UE for receiving a specific DL RS.

Alternatively, a method of directly configuring/instructing, by the basestation, beamforming vectors/coefficients to be applied by the UE whentransmitting the precoded SRS to the UE may be applied (e.g., a casewhere the base station may acquire the information based on channelreciprocity, for example, according to another specific method, and thelike). The base station may directly inform the beamformingvectors/coefficients to the UE through a control channel such as aspecific DCI triggering the transmission of the corresponding precodedSRS or through a separate specific layer 1 (L1), layer 2 (L2), and/orlayer 3 (L3) (e.g. semi-static by RRC) signaling.

As a result, the Type 1 UL-LA UE to which the operation is applicablemay be limited as i) “channel-reciprocity calibrated UE (e.g., NR (or5G) UE, 3GPP release-15 and later UEs, etc.)”, ii) “UE not performingfully-digital-beamforming in the transmitter (TX) (and/or transmitterand receiver (TRX)) antennas/ports of the UE”, iii) “UE applyinganalog-beamforming to UL TX ports”, and/or iv) “UE operating in TDD”.

In addition/alternatively, the UE provides its own specific capability(e.g., whether or not the Type 1-related support is available, etc.)associated with this to the base station in advance, and thus, the aboveoperation/process may be configured/initiated.

2) Type 2 UL-LA UE (UL-LA process operation by starting Precoded SRStransmission)

Regarding such an SRS, the UE may be defined/configured to transmit aNon-precoded SRS. In this case, the base station measures thenon-precoded SRS of the specific port(s) to determine the proposed U1and/or U2 information. Thereafter, the base station transmits a ULscheduling grant (e.g., in case of U1, may be separately transmitted tothe UE via a separate DCI (field) or a separate message container forspecific control information delivery (by L1 and/or L2 signaling)including the determined U1 and/or U2 information. Accordingly, there isdisclosed frequency-selective UL-MIMO scheduling considered in thepresent invention.

As such, a type, in which a UL link adaptation (UL-LA) process isinitiated only by transmission of a specific non-precoded SRS and thebase station informs the final UL precoder such as U1 and/or U2, etc.determined by measuring the non-precoded SRS of the specific port(s) tothe UE when the UL scheduling, is referred to as a Type 2 UL-LAoperation (or UE).

More specifically, this Type 2 UE may mean UE in which TX (and/or TRX)antennas/ports of the UE are fully-digital-beamformable.

As a result, the Type 2 UL-LA UE to which the operation is applicablemay be limited as i) “channel-reciprocity non-calibrated UE” (e.g.,LTE/LTE-A UE, UE up to 3GPP release-14), ii) “fully-digital-beamformingpossible UE”, and/or iii) “UE operating in FDD (and/or TDD)”, etc.

In addition/alternatively, the UE provides its own specific capability(e.g., whether or not the Type 2-related support is available, etc.)associated with this to the base station in advance, and thus, the aboveoperation/process may be configured/initiated.

3) Type 3 UL-LA UE (UL-LA process operation by receiving specificbeamforming information from the base station by starting (S1 ports)Non-precoded SRS transmission and initiating (S2(<=S1)) ports precodedSRS transmission by applying the received information

Alternatively, regarding such an SRS, the UE may be configured/indicatedto transmit a specific (S1 ports) non-precoded SRS primarily (with along-term period) by the UE so that the base station derives primarybeamforming vectors/coefficients. In addition, the base stationinstructs the beamforming vectors/coefficients to the UE to transmit asecondary specific (S2(<=S1) ports) precoded SRS. In this case, there isonly a difference in that a coarse beam estimation operation by theprimary non-precoded SRS is added. In other words, the base stationmeasures the (S2(<=S1) ports) Precoded SRS to determine the proposed U1and/or U2 information. Thereafter, the base station transmits a ULscheduling grant (e.g., in case of U1, may be separately transmitted tothe UE via a separate DCI (field) or a separate message container forspecific control information delivery (by L1 and/or L2 signaling)including the determined U1 and/or U2 information. Accordingly, there isdisclosed frequency-selective UL-MIMO scheduling considered in thepresent invention.

At this time, as a method for configuring/instructing to the UE to applythe beamforming vectors/coefficients derived (by receiving thenon-precoded SRS in the base station) to the corresponding precoded SRS,the base station may directly inform the beamformingvectors/coefficients to the UE through a control channel such as aspecific DCI triggering the transmission of the corresponding precodedSRS or separately specific L1, L2, and/or L3 (e.g., semi-static by RRC)signaling.

As such, a type, in which transmission of a specific non-precoded SRS isincluded and transmission of a specific precoded SRS is initiated byreceiving the information related to the application of the beamformingfrom the base station and applying the received information, and thebase station informs the final UL precoder such as U1 and/or U2, etc.determined by measuring the precoded SRS to the UE when UL scheduling isreferred to as a Type 3 UL-LA operation (or UE).

More specifically, this Type 3 UE may mean UE in which TX (and/or TRX)antennas/ports of the UE are fully-digital-beamformable.

As a result, the Type 2 UL-LA UE to which the operation is applicablemay be limited as i) “channel-reciprocity non-calibrated UE”, ii) “UEnot performing fully-digital-beamforming in the TX (and/or TRX)antennas/ports of the UE”, iii) “UE applying analog-beamforming to UL TXports”, and/or iv) “UE operating in FDD (and/or TDD)”.

In addition/alternatively, the UE provides its own specific capability(e.g., whether or not the Type 3-related support is available, etc.)associated with this to the base station in advance, and thus, the aboveoperation/process may be configured/initiated.

In addition/alternatively, a specific SRS resource(s) is configured inadvance in the UE, and the UE may be configured to transmit a separateprecoded SRS based on each SRS resource configuration. At this time, thenumber of SRS ports per SRS resource may be one or more.

That is, the UE may perform the SRS transmission based on the number ofSRS ports corresponding to each SRS resource and correspondingconfiguration.

At this time, the beamforming vectors/coefficients to be applied at thistime are selected arbitrarily (eNB-transparently, randomly) or selectedaccording to the indication of the base station and the UE may transmitthe precoded SRS for each SRS resource. In this case, the base stationfirst selects a SRS resource with the highest reception quality throughthe SRS measurement for each SRS resource and derives the U1 and/or U2with respect to the SRS ports in the SRS resource and indicates the U1and/or U2 to the UE. That is, the base station derives the U1 and/or U2to be applied to the SRS ports in the corresponding SRS resource toindicate the derived U1 and/or U2 to the UE.

In this case, a UL scheduling grant (e.g., U1 and/or SRI) including notonly the proposed U1 and/or U2 information but also the best SRSresource indicator (e.g., U1 and/or SRI may be separately transmitted tothe UE through a separate DCI (field) or a separate message containerfor transmitting specific control information (by L1, L2, and/or L3(e.g., semi-static by RRC) signaling)) is transmitted. Accordingly,there is disclosed a frequency-selective UL-MIMO scheduling consideredin the present invention.

In other words, the base station configures multiple SRS resources tothe UE, and the UE may transmit a precoded SRS having different beamdirections for each SRS resource to the base station. In addition, thebase station informs the UE of the uplink scheduling grant (DCI)including the SRI and the precoding indication (e.g., U1 and/or U2, ortransmitted precoding matrix indicator (TPMI)) transmitted by the UE inthe previous time instance. In this case, the precoding indication maybe used to indicate preferred precoder over the SRS ports in theselected SRS resource by the SRI.

For example, if a specific SRS resource is configured to transmit a1-port SRS, when the UE implements X transmission antenna(s)/port(s),the UE may be defined/configured to transmit a type of “rank 1 precodedSRS” by applying specific X-by-1 beamforming vector/coefficients.

Similarly, if the specific SRS resource is configured to transmit av(>1)-port SRS, when the UE implements X(>=v) transmissionantenna(s)/port(s), the UE may be defined/configured to transmit a typeof “rank v precoded SRS” by applying specific X-by-v beamformingvector/coefficients.

That is, there may be a characteristic of the corresponding “SRS portnumber=(target) rank number” configured for each SRS resource.

Accordingly, when the base station configures/instructs the SRI to theUE, it may be recognized that the SRI includes a meaning of a kind ofrank indication. In addition, the SRI may be defined/configured to beapplied at the time of interpretation of other fields within thecorresponding UL grant based on the indicated rank.

In other words, the number of SRS antenna ports may be predefined orconfigured for each SRS resource (for example, by higher layer signalingsuch as RRC), and when the base station transmits the UL grant includingthe SRI to the UE, the number of ranks for transmission of uplink data(e.g., PUSCH) of the UE may be determined as the number of antenna portscorresponding to the SRS resources indicated by the SRI.

As another example, the operation may be defined/configured/indicated sothat a precoder applied to the corresponding implicitly-indicated SRSresource index is applied when the UL transmission by automaticallyinterworking which SRS resource index is indicated through the rankindication (field) indicated by the UL grant and the like without theinformation indication of the SRI (however, it is preferable that onlyone SRS resource associated with a specific rank is limited to one toone linkage).

Alternatively, as a more flexible UL scheduling related signaling, thebase station may be defined/configured to independently inform the rankindication as well as the SRI to the UE. This is a case where one ormore SRS resources (s) may be configured for a specific target rank. Thereason why the base station configures a plurality of SRS resources fora certain rank is that the UE applies different beamformingvectors/coefficients with respect to the same rank and tries to transmitthe SRS several times. That is, the base station measures the precodedSRS with different beam coefficients for the same rank to provide theflexibility to determine and instruct which UL precoder is moreadvantageous (in terms of performance) even when the corresponding rankis finally selected.

In addition/alternatively, when the UE applies specific “beamformingvectors/coefficients” to the corresponding precoded SRS, the UE may beconfigured to apply the “beamforming vectors/coefficients” as thebeamforming vectors/coefficients which are common over the transmissionband as a wideband attribute.

In addition, an operation may be defined or configured to the UE totransmit a subband precoded SRS for the corresponding SRS resource inthe form of applying different/independent beamformingvectors/coefficients in a specific subband (or PRB (group)) unitfrequency-selectively over the transmission band.

In addition, That is, the base station may designate whether thewideband precoding or subband precoding is applied to the precoded SRSto the UE by L1 (by DCI), L2 (by MAC control element (CE)), and/or L3(by RRC) signaling.

Even when specific “frequency-selective (subband) beamformingvectors/coefficients” are applied when transmitting specific precodedSRS, the following operation may be defined or configured to the UE.

i) The base station informs the UE of the corresponding“frequency-selective (subband) beamforming vectors/coefficients”(separately or when indicating/triggering the corresponding SRStransmission) so that the UE follows the information.

ii) The UE may select arbitrarily (eNB-transparently, randomly) totransmit (frequency-selective) precoded SRS for each SRS resource.

iii) The UE may find (alternatively, find and report) the best“serving-beam” by measuring Y (e.g., Y=1) DL specific RS (e.g., RRM-RS,BRS, BRRS, etc.) ports transmitted by the base station. In addition, theUE may determine a X-by-Y precoder/beamformer vector/coefficientfrequency-selectively (as a dimension by the number X of TRXantennas/ports of the UE) for each subband when the UE determines itsown (paired) best “Rx-receiving-beam” to apply the determined X-by-Yprecoder/beamformer vector/coefficient reversely (e.g., takingHermitian) when transmitting the corresponding precoded SRS.

When such RRM-RS type (e.g., BRS, BRRS, etc.) is used, it is limited toY=1, so that the transmission SRS of the UE may be limited to only arank 1 precoded SRS.

Further, it is possible to explicitly indicate whether to calculate theX-by-Y precoder for a specific RRM-RS (e.g., BRS, BRRS, etc.) signalingtype. In addition, the specific RRM-RS (e.g., BRS, BRRS, etc.) (ports)may be indicated as a quasi co-located (QCL) signaling type.

iv) The UE may determine its own (paired) best “Rx-receiving-beam” bymeasuring Z(>=1) DL specific (for CSI measurement) RS (e.g., CSI-RS)ports transmitted from the base station. In this case, the UE determinea X-by-Z precoder/beamformer vector/coefficient frequency-selectively(as a dimension by the number X of TRX antennas/ports of the UE) foreach subband and apply the determined X-by-Z precoder/beamformervector/coefficient reversely (e.g., taking Hermitian) when transmittingthe corresponding precoded SRS. The operation may be defined orconfigured to the UE.

In other words, the UE may transmit the SRS using spatial filteringwhich is the same as spatial filtering used for the reception of aspecific DL RS when transmitting the SRS transmission in the specificsubband. That is, the UE may implement spatial filtering that is optimalfor DL RS reception for each DL RS, and the base station may indicatethe UE to perform transmission of a SRS resource in the specific subbandusing the same spatial filtering as the spatial filtering used by the UEfor receiving a specific DL RS.

When CSI-RS is used as such, it may be limited to Z>1, or may beflexibly defined or configured to the UE as Z>=1. The reason for notusing the above RRM-RS (e.g., BRS, BRRS) is that it may be limited toonly rank 1 because it may be limited to a single port, so it iseffective to use CSI-RS to support rank >1.

Further, the UE may be explicitly indicated to calculate the X-by-Zprecoder for which specific CSI-RS (port(s)). In addition, the specificCSI-RS (port(s)) may be indicated as a QCL signaling type. Inaddition/alternatively, the UE may be defined/configured that thecorresponding CSI-RSs (port(s)) have a QCL linkage with which RRM-RS(e.g., BRS, BRRS) together or separately.

It will be apparent that all (or some) of the proposed operationsassociated with the SRS may be applied to the schemes (e.g., a singlePMI (TPMI), precoder based scheme) which do not follow the U1 and/or U2structure. For example, to determine a specific single UL precoder U,the operations may be modified/applied as operations such as giving aspecific UL precoder indication for non-precoded/precoded SRStransmissions (by the SRS resource(s) based configuration), or the like.

The expression “SRS resource” is a name given for convenience and assuch, the SRS resource may be signaled/indicated to the UE in a form inwhich a specific index is actually given per SRS resource unit.Alternatively, the operation of the present invention may be applied byanother name/parameter which replaces the concept of the “SRS resource”by binding specific/some/virtualized SRS ports(s) grouped by specificgrouping with respect to (entire) SRS ports transmittable by the UE.

Additional Proposals

In such an operation, semi-open loop (OL) UL transmission may beconfigured/indicated to the UE in the form of deleting all U2information for each subband.

For example, the base station may transmit an UL grant of a type withoutthe U2 information to the UE as described above through a specific(separate) signaling (or using one of the U1 indexes) and this mayoperate as instructing the UE to perform specific (semi-)OL ULtransmission.

When the UE is configured/instructed as described above, the UE mayignore the information even if the U2 information exists in the ULgrant.

Alternatively, when the UE is configured/directed as described above,the payloads where U2 information may exist may be deleted from the(UL-related) DCI. In this case, the UE may be defined or configured toperform blind detection (BD) for different payload sizes in a form inwhich the total payload size of the corresponding DCI is reduced againstthe case the U2 information exists.

Further, the (semi-)OL UL transmission may be instructed in a form ofdeleting only the precoder(s) information in the direction of a specific(spatial) dimension of U1 and/or U2.

For example, when the UE determines that the channel change isinsignificant in the vertical direction and the channel change isrelatively severe in the horizontal direction, the UI and/or U2information may be indicated in conjunction with UL scheduling in a formin which specific precoder(s) information of a horizontal component isdeleted (or ignored or replaced with other information). In this case,the UE may UL-transmit the corresponding part by applying an OL schemesuch as precoder cycling according to a specific pre-defined/indicatedOL-precoding scheme. In addition, the UE may perform UL transmission byapplying the precoder(s) part as instructed for the specific (spatial)dimension for which the U1 and/or U2 information is provided.

As described above, when the specific (spatial) dimension precoder(s)information is deleted and indicated, the payload part may be deleted.In this case, the UE may be defined or configured to perform the BD fordifferent payload sizes in a form in which the overall payload of thecorresponding DCI is reduced in comparison with the conventional one.

Mapping of the payload sizes of the U1 and U2 and the correspondinginformation as above may be defined to correspond to the number of UL(link adaptation) specific RS (for example, SRS) ports of thecorresponding UE, which are transmitted in advance (in link with themapping) or configured/instructed to the UE.

UL MIMO Design Framework

In LTE UL MIMO, the network indicates precoder to UE, then UE transmitsthe DMRS and data by applying the indicated precoder. In NR UL MIMO,precoded RS based transmission where the same precoder is applied toboth the DMRS and the physical data channel is still desirable in termsof DMRS overhead. The reason is that the transmission rank would besmaller than the number of TXRUs due to lack of scatterers in mostcases.

Therefore, it is preferable that the precoded RS based transmissionwhere the same precoder is applied to both the DMRS and the physicaldata channel becomes a baseline in NR UL MIMO.

Regarding transmission technique, it was agreed to support UL DMRS basedspatial multiplexing (single user (SU)-MIMO/MU-MIMO). UL coordinatedmulti-point (CoMP) transmission may also be supported. That is, ULreception point(s) may be transparent to UE.

For UL SU-MIMO, both an open loop (OL) technique where no precoderinformation is signaled by the network to the UE and a semi-open-loop(OL) technique where a part of precoder information is signaled by thenetwork to the UE may be considered in addition to a conventional closedloop technique where full information (i.e., PMI and RI) of precoder issignaled by the network to the UE. OL and semi-OL MIMO may be usefulwhen full or partial DUUL reciprocity is valid in TDD. UL MU-MIMO may bebased on a closed loop operation, but is not limited thereto.

The UL MIMO transmission techniques may be classified with respect toexistence and completeness of the precoder information signaled from thenetwork to the UE as follows:

-   -   Closed loop: Full precoder information is signaled to UE    -   Open loop: No precoder information is not signaled to UE    -   Semi-open loop: A part of precoder information is signaled to UE

Further, it was agreed to support at least 8 orthogonal DL DMRS portsfor both DL SU-MIMO and DL MU-MIMO. Similarly to DL, the reference of ULmay be LTE so that we propose to support at least 4 orthogonal DMRSports for both UL SU-MIMO and UL MU-MIMO as the baseline. From SU-MIMOperspective, no clear motivation of supporting higher layers than LTEexists by considering the possibility of a higher rank in practicalenvironments (i.e., limited number of dominant rays at high frequencybands and limited number of TXRUs at the UE). However, when forwardcompatibility is considered, increasing the maximum layers from thebeginning may be considered (e.g. 8 layers for UL SU-MIMO by takinglarge UE types into account). From MU-MMO perspective, NR has clearmotivation of achieving higher order MU-MIMO to achieve target spectralefficiency. However, it would be desirable to support MU multiplexinglayers exceeding certain number (e.g. 4 or 8) by utilizingnon-orthogonal DMRS ports (e.g. scrambling sequence) in order to managethe DMRS overhead within a reasonable range.

Therefore, it is preferable that a least 4 orthogonal UL DMRS ports aresupported for both SU-MIMO and MU-MIMO.

With regard to the number of codewords for spatial multiplexing,supporting up to two codewords as LTE may be reasonable by considering atrade-off relationship between link adaptation flexibility and thecontrol signaling overhead.

Therefore, it is preferable that for NR UL MIMO, up to two codes arebasically supported.

Frequency Selective Proceeding for UL MIMO

There was an agreement that cyclic prefix (CP)-OFDM without specifiedlow-peak to average power ratio (PAPR)/cubic metric (CM) technique(s) isrecommended to be supported for uplink NR waveform for at least up to 40GHz for enhanced Mobile BroadBand (eMBB) and ultra-reliable low latencycommunication (URLLC) services.

Considering a CP-OFDM waveform and an increased supportable systembandwidth in NR, frequency selective precoding may be considered to beintroduced for UL MIMO. However, the increased control channel overheaddue to the indicated subband PMIs may be a critical problem for applyingsuch frequency selective UL-MIMO precoding. Although it may beconsidered to signal multiple PMIs separately from UL-related DCI and toinclude a pointer field in the DCI for indicating such signaling, thiskind of two-step approach may not be desired due to latency forproviding the full information of subband-wise multiple PMIs in a firststep. In other words, a motivation of introducing such frequencyselective UL precoder is to achieve fast UL link adaptation exploitingthe frequency domain as well, so that the full set of precoderinformation is desired to be delivered instantaneously to the UE whenthe set of precoder information is scheduled for the UL transmission.

To resolve the control channel overhead issue for frequency-selectiveUL-MIMO scheduling, applying the dual codebook structure as in DLsimilarly to the UL case (e.g., 4-Tx case) needs to be investigated.Considering the agreed CP-OFDM structure for UL, a final UL precoder Wper subband may be decomposed into a wideband PMI component W_1 and thecorresponding subband PMI component W_2. Then, in the UL scheduling DCI,the W_1 information is enough to be included once, and multiple W_2 sare required to be included depending on the scheduled RB region givenby a resource allocation field in the same DCI. How to define thecodebook for W_1 and W_2 is for further study, but the baseline shouldbe reusing Rel-12 DL 4-Tx codebook. The existing LTE 2-Tx DL codebookmay be reused as it is for the 2-Tx UL case and the whole per-subbandPMIs need to be provided in the UL scheduling grant. It should also beinvestigated whether the DFT spread OFDM (DFT-S-OFDM) based UL-MIMOprecoder is supported and in that case, how to configure the UE witheither using the CP-OFDM based UL precoder or using the DFT-S-OFDM basedUL precoder as discussed above.

That is, the UE may be configured with at least one of CP-OFDM-basedcodebook 1 (e.g., the dual codebook structure) and DFS-S-OFDM basedcodebook 2 (e.g., cubic-metric preserving codebook, etc.) from the basestation. In addition, the UE may be configured with on which codebookbased UL precoding is to be performed based among the above codebooksfrom the base station by L1 (e.g., by DCI), L2 (e.g., by MAC CE), and L3(e.g., by RRC).

Particularly, when the CP-OFDM-based UL transmission isconfigured/instructed, the UE may be configured/instructed (and/orswitched) with one of codebook 1 and codebook 2 from the base stationand may apply the configured/instructed codebook and conversely, whenthe DFS-OFDM based UL transmission is configured/instructed, it may belimited that the UE may continuously apply only codebook 2. The reasonis that under the DFS-S-OFDM scheme, the application of codebook 1 maybe inappropriate in that the application of codebook 1 greatly amplifiesthe PAPR and the like.

More particularly, which codebook is applied in conjunction with aspecific rank value may be defined or configured to the UE. For example,in the case of transmission of rank X (for example, X=1), codebook 2 maybe defined to be applied or may be configured to the UE in terms oftransmission power, such as PAPR issues. On the contrary, in the case ofrank Y (for example, Y=2) or more, codebook 1 is configured (forexample, in general, UE other than a cell-edge region) to be applied tobe defined or configured to the UE to apply the precoder capable ofmaximizing throughput rather than an aspect of the transmission power.

When such operations are applied, when the rank is indicated through theUL grant or the like, the UE may automatically analyze/apply theindicated PMI/precoder while applying the different codebook as above inconjunction with the indicated rank.

In the above description, as an example, an operation is described, inwhich a specific codebook (for example, codebook 1 or codebook 2, . . .) is adopted in conjunction with being configured based on a specificwaveform (e.g., based on the CP-OFDM or DFS-S-OFDM).

However, the present invention is not limited thereto, and suchoperations may be defined or configured/instructed to the UE so that theUE may initiate the UL transmission by applying a specific codebookamong specific candidate codebook 1 (e.g., a DFT-based codebook),codebook 2 (e.g., a Grassmannian codebook), and codebook 3 (e.g., ahouseholder codebook) under the instruction of the base stationregardless of the specific waveform at the time of the UL transmissionby the UE.

As a more specific embodiment, candidate codebook 1, which is moresuitable when arrangement/spacing between antennas according to a UEantenna configuration are implemented in relatively uniform and/orclosely-spaced form, may be defined or configured to the UE in aspecific DFT-based codebook (e.g., a dual codebook structure includingan LTE-A codebook) using a DFT vector or the like. Further, candidatecodebook 2, which is more suitable when the arrangement/spacing betweenthe antennas according to the UE antenna configuration is relativelyirregular or widely-spaced, may be defined/configured in a codebook formoptimized so as to maximally maintain an intercede vector equaldistance, such as the Grassmannian codebook. In addition, candidatecodebook 3 may be defined or configured to the UE in a form of aspecific hybrid type codebook, for example, the householder codebook asa form made by extracting some code vectors among different codebookshaving different attributes and purposes, which include codebook1 andcodebook 2 (according to the UE antenna configuration).

As a result, when the UE accesses a specific base station in advance,the UE may be defined or configured to perform capability signaling,through a UE capability signaling, which codebook which is at least oneamong (the) specific candidate codebooks which may be applied at thetime of the UL transmission is implemented or supported. In addition/or,when the number of codebooks which are implemented/supported as such istwo or more, the UE may notify the base station which codebook of thetwo codebooks the UE prefers (may provide subdivided preferenceinformation in such a manner of giving weighting). In this case, whichcodebook is more suitable may be determined based on the implementedantenna configuration characteristic of the corresponding UE and thereis an effect that information related with a codebook showing a moreadvantageous effect in terms of performance of the codebooksimplemented/supported as such is provided to the base station.

In addition, based on the information, the base station allows the UE toconfigure/indicate the codebook to be applied at the time of the ULtransmission. In this case, among the codebooks which the UE performsthe capability signaling to implement/support, a codebook which is notimplemented/supported by the corresponding base station may also exist.In this case, the base station may configure the UE to use only thecodebook implemented/supported thereby (regardless of thecodebook-to-codebook preference information reported by the UE).Alternatively, even if the base station is also capable ofconfiguring/instructing a plurality of codebooks to the UE (that is,even if all of the codebooks are implemented), the base station mayconfigure/indicate the specific codebook to commonly applied to becell-specific or UE group-specific by synthetically considering acodebook implementation/support status and/or codebook preference statusof the plurality of UEs accessing the corresponding cell (for example,for the purpose of facilitating UL MU-MIMO transmission or the like).

In the method in which the base station configures/instructs thecorresponding UE to apply the specific codebook at the time of the ULtransmission, a relatively quasi-static configuration method by RRCsignaling (and/or MAC CE signaling) or the like is also applicable. Asdescribed above, it is possible to dynamically indicate which specificcodebook is to be applied to the UE by a relatively more dynamicsignaling/indication in conjunction with a specific UL scheduling grant.Such a dynamic indication may be implicitly and/or explicitly indicated(in conjunction with feature field information) via a specific field inthe control signaling, such as the corresponding UL grant.

More particularly, as mentioned above, which codebook is to be appliedin conjunction with a specific rank may be pre-defined or configured tothe UE. For example, when an UL grant scheduling rank 1 UL transmissionis transmitted, the UE may be continuously defined or configured to theUE to initiate the UL transmission by applying a specific codebook(e.g., codebook 2) associated therewith. Further, when an UL grantscheduling rank X (for example, X>1) UL transmission is transmitted, theUE may be continuously defined or configured to the UE to initiate theUL transmission by applying a specific codebook (e.g., codebook 1)associated therewith.

Thus, if supported, all subband UL-MIMO precoder(s) is(are) preferablyinstantaneously provided to the UE within the UL scheduling grant and inthis case, a wideband component may be included only once to reducecontrol channel overhead.

Precoded SRS Based Transmission for UL MIMO

For UL link adaptation (LA), LTE may configure the UE to transmit SRSwith different multiple sets of SRS related parameters, where the UE mayapply implemented specific precoding/selection on SRS port(s) especiallywhen the configured number of SRS port(s) is smaller than the UE's totaltransmit (Tx) antenna ports. Compared to Rel-13/14 enhanced (e) FD-MIMObeamformed CSI-RS based operations, precoded/beamformed SRStransmissions for UL LA need to be thoroughly investigated in NR. Forconvenience of description, there may be three UE types in terms of theUL LA process as follows:

1) Type 1 UE (UL-LA Initiated with Transmitting Precoded SRS(s))

-   -   The UE may be configured with one or more SRS resources and        beamforming indicated by transmit and reception point (TRP) or        TRP transparent beamforming is applied to the SRS transmission        on each SRS resource.    -   Based on measuring UE's transmitted precoded SRS resource(s),        the TRP determines SRS resource indicator (SRI) (in case of        multiple configured SRS resources), MCS and/or a precoder across        the SRS port in the SRI are determined and indicates the SRI,        the MCS, and the precoder to the UE when the UL scheduling grant        is delivered to the UE.

2) Type 2 UE (UL-LA Initiated with Transmitting Non-Precoded SRS(s))

-   -   The UE may be configured with one SRS resource and the UE        transmits non-precoded SRS.    -   Based on measuring UE's transmitted non-precoded SRS        resource(s), the TRP determines the MCS and/or the precoder        across the SRS port in the SRI are determined and indicates the        MCS and the precoder to the UE when the UL scheduling grant is        delivered to the UE.

In the case of 4-Tx UE and CP-OFDM, the above dual codebook structure isused for the frequency-selective UL-MIMO precoder.

3) Type 3 UE (UL-LA initiated with transmitting non-precoded SRS(s) andtransmission of precoded SRS according to TRP's indication)

-   -   Based on measuring UE's non-precoded SRS K₁ port(s), the TRP        determines coarse beamformer and indicates it to the UE to be        applied on transmitting the following precoded SRS K₂(≤K₁)        ports(s). Then, based on measuring UE's transmitted precoded SRS        port(s), the TRP determines MCS and/or precoder, and indicates        them when UL scheduling grant is delivered to the UE.

Based on the above classified types that may be reported by the UE,different UL-LA processes may be configured to be UE-specific, includingwhich types of SRS transmission is performed by the UE. Regardingprecoded SRS transmission cases (e.g., Type 1 and/or Type 3), multipleSRS resources may be configured to UE, where the UE transmitsdifferently-beamformed SRS port(s) on each configured SRS resource. TheTRP may indicate such beamformer information to the UE, or the UE isallowed to apply the TRP-transparent beamformer for the SRStransmission. Then, when UL scheduling grant is given to the UE, the TRPmay indicate the SRS resource indicator for which the UE should applythe same beamformer used on the SRS transmission corresponding to theindicated SRS resource, for the scheduled UL transmission. Further, onthe selected SRS resource, the TRP may further indicate digitalprecoding information (e.g., UL PMI) over the SRS port(s) within theindicated SRS resource. It should be noted that the configured number ofSRS ports for each SRS resource may be interpreted as a target rank inUE's UL transmission. Therefore, the TRP may configure multiple SRSresources, each corresponding to the different rank to cover rank 1 to 4(e.g., v-port SRS configured for v-th SRS resource (where v=1, 2, 3,)).

Accordingly, procedures related with the non-precoded and/or precodedSRS transmission should be further investigated based on different UEtypes in terms of the UL link adaptation process.

FIG. 13 is a diagram illustrating a method for transmitting andreceiving an uplink according to an embodiment of the present invention.

In FIG. 13, the operation of the present invention is simplyillustrated, and a more detailed description thereof may follow theaforementioned operation.

Referring to FIG. 13, the UE receives downlink control information (DCI)from the base station (S1303).

The DCI may include an SRS Resource Indication (SRI), a precodingindication (e.g., U1 and/or U2, or TPMI) and/or a rank indication (e.g.,TRI).

For example, the precoding indication may be divided into a firstprecoding indication (i.e., U1) having a wideband attribute and a secondprecoding indication (U2) indicated for each subband. In this case, thesecond precoding indication U2 may be transmitted while being jointlyencoded with uplink resource allocation information scheduled to the UE.That is, the second precoding indication U2 may be configured/indicatedtogether in link with a UL RA field.

The UE transmits an uplink to the base station by applying precodingindicated by the precoding indication on an antenna port of an SRStransmitted in an SRS resource selected by the SRI (S1304).

The number of ranks for the uplink transmission may be explicitlyindicated by the DCI or implicitly determined as the number of antennaports of the SRS transmitted in the SRS resource selected by the SRI inthe DCI.

Meanwhile, before step S1303, the UE may receive a downlink referencesignal (DL RS) (e.g., CSI-RS, etc.) from the base station (S1301).

Further, the UE may transmit the precoded SRS for each of one or moreSRS resources configured for the UE to the base station (S1302).

In this case, the base station may select an SRS resource having thehighest reception quality through SRS measurement for each SRS resourceand indicate the UE by deriving the precoding indication (for example,U1 and/or U2, or TPMI) with respect to the SRS port(s) in the selectedSRS resource.

Further, a beamforming vector and/or beamforming coefficient applied fortransmission of the precoded SRS may be configured by the base stationthrough a control channel signaling or arbitrarily determined by the UE.

Further, the beamforming vector and/or beamforming coefficient appliedfor the precoded SRS transmission in the SRS resource may be determinedbased on a beamforming vector and/or beamforming coefficient used forreception of the DL RS (e.g., CSI-RS etc.).

More specifically, the UE measures the DL RS transmitted by the basestation to find (and also report) a best “serving-beam”. In addition,the UE may determine a paired best “Rx-receiving-beam” thereof for thebest “serving-beam”. Further, the UE may transmit the precoded SRS byapplying the corresponding beamforming vector/coefficient(s), whentransmitting the precoded/beamformed SRS, by reversing (e.g., takingHermitian) the best “Rx-receiving-beam” by using a DL/UL channelreciprocity characteristic (or a beam pair link). That is, the precodedSRS transmission may be performed with spatial filtering which is thesame as spatial filtering used for the reception of a specific DL RS(e.g., the best “serving-beam”).

When the DL-RS is the CSI-RS, the CSI-RS resource used for determiningthe beamforming vector and/or beamforming coefficient applied for theprecoded SRS transmission is indicated by the base station.

In addition, the precoding SRS transmission which the UE performs in theSRS resource may be performed independently for each subband.

For example, for the precoded SRS transmission in the SRS resource, anindependent beamforming vector and/or beamforming coefficient may beapplied for each subband.

Further, the beamforming vector and/or beamforming coefficient appliedfor the SRS transmission precoded for each subband in the SRS resourcemay be determined based on a beamforming vector and/or beamformingcoefficient used for reception of the DL RS (e.g., CSI-RS etc.).

More specifically, the UE measures the DL RS transmitted by the basestation to find (and also report) the best “serving-beam”. In addition,the UE may determine a paired best “Rx-receiving-beam” thereof for thebest “serving-beam”. Further, the UE may transmit the precoded SRS foreach subband by applying the corresponding beamformingvector/coefficient(s), when transmitting the precoded/beamformed SRS, byreversing (e.g., taking Hermitian) the best “Rx-receiving-beam” by usinga DUUL channel reciprocity characteristic (or a beam pair link). Thatis, the precoded SRS transmission may be performed with spatialfiltering which is the same as spatial filtering used for the receptionof a specific DL RS (e.g., the best “serving-beam”) in a specificsubband.

In this case, when the DL-RS is the CSI-RS, the CSI-RS resource used fordetermining the beamforming vector and/or beamforming coefficientapplied for the precoded SRS transmission is indicated by the basestation.

The following technologies are discussed for NR UL/DL MIMO.

The following downlink first layer (L1)/second layer (L2) beammanagement procedure is supported within one or moretransmission/reception points (TRPs).

-   -   P-1 is used to enable UE measurements on different TRP Tx beams        to support selection of TRP transmission (Tx) beam(s)/UE        reception (Rx) beam(s).

For beamforming in the TRP, P-1 includes intra-TRP/inter-TRP Tx beamsweeps from a set of different beams.

For the beamforming in the UE, P-1 includes a UE Rx beam sweep from theset of different beams.

The TRP Tx beam and the UE Rx beam may be jointly or sequentiallydetermined.

-   -   P-2 is used to enable UE measurements on different TRP Tx beams        so as to change inter/intra-TRP Tx beam(s).

A set of beams smaller than P-1 may be used for beam refinement aspossible.

P-2 may be regarded as a special case of P-1.

-   -   P-3 is used to enable UE measurements on the same TRP Tx beam so        as to change the UE Rx beam when the UE uses the beamforming.

Intra-TRP beam measurement and inter-TRP beam measurement may beperformed in the same procedure. The UE may not know whether the TRP Txbeam is the intra-TRP beam or the inter-TRP beam.

The procedures of P-2 and P-3 may be performed jointly and/or multipletimes (e.g., the TRP Tx/UE Rx beam may be changed at the same time).

The UE may manage multiple Tx/Rx beam pairs.

Assistance information from another carrier is being discussed in a beammanagement procedure.

The procedure may be applied to any frequency band. Further, theprocedure may be used for single/multiple beam(s) for each TRP.

-   -   Uplink beam management is discussed in new radio (NR) access        technology (RAT).

A procedure similar to downlink beam management may be defined. Forexample, the procedure is described below.

U-1 is used to enable TRP measurements on different UE Tx beams in orderto support selection of the UE Tx beam(s)/TRP Rx beam(s).

This may not necessarily be used in all cases.

U-2 is used to enable TRP measurements on different TRP Rx beams so asto change/select the inter/intra-TRP Rx beam(s).

U-3 is used to enable TRP measurements on the same TRP Rx beam so as tochange the UE Tx beam when the UE uses the beamforming.

-   -   Information related to Tx/Rx correspondence is supported.    -   The uplink beam management is discussed based on:

Physical random access channel (PRACH)

Sounding reference signal (SRS)

Demodulation reference signal (DM-RS)

Other channels and reference signals are not excluded.

-   -   The uplink beam management procedure is discussed in        consideration of the Tx/Rx beam correspondence:

When the TRP and the UE have the Tx/Rx beam correspondence

When the TRP does not have the Tx/Rx beam correspondence and/or the UEdoes not have the Tx/Rx beam correspondence

-   -   The CSI-RS supports downlink Tx beam sweeping and UE Rx beam        sweeping.

The CSI-RS may be used in P1, P2, and P3.

-   -   The NR CSI-RS supports the following mapping structure.

N_P CSI-RS port(s) may be mapped for each (sub) time unit.

Throughout the (sub) time unit, the same CSI-RS antenna port may bemapped.

Herein, “time unit” may be represented by N>=1 OFDM symbols withinconfigured/referred numerology.

The OFDM symbols constituting one time unit may or may not becontinuous.

A port multiplexing method (e.g., frequency division multiplexing (FDM),time division multiplexing (TDM), code division multiplexing (CDM), oranother combination) may be used.

Each time unit may be divided into sub-time units.

The division method may adopt, for example, TDM, interleaved frequencydivision multiple access (IFDMA), and OFDM symbol-level division to anOFDM symbol length (i.e., a subcarrier spacing greater than thesubcarrier spacing) which is equal to or shorter than a reference OFDMsymbol length and further, other methods are not excluded.

Such a mapping structure may be used to support multiple panel/Txchains.

CSI-RS mapping options for Tx and Rx beam sweeping are described below.

Option 1: The Tx beam(s) are the same across the sub-time units withineach time unit. The Tx beam(s) are different for each time unit.

Option 2: The Tx beam(s) are different for each sub-time unit withineach time unit. The Tx beam(s) are the same across the time unit.

Option 3 (Combination of Option 1 and Option 2): The Tx beam(s) are thesame across the sub-time units within each time unit. The Tx beam(s) aredifferent for each sub-time unit within another time unit.

Only Tx sweeping or Rx sweeping may be possible.

Another option is not ruled out.

The mapping scheme described above may or may not be configured as oneor multiple CSI-RS resource configurations.

Multiple SRS Resource Types for Beam Management

-   -   A specific SRS resource configured for distinguishing A, B, or C        UL-LA UEs discussed/mentioned above and/or for corresponding        correspondence operations may be classified/distinguished into        “Type 1 SRS resource”. It can be seen (and characterized) that        the specific SRS resource may be configured for achieving fast        link adaptation for UL data scheduling.

A set of one or more ‘SRS port(s)’ may be configured within Type 1 SRSresource.

In this case, for example, a specific analog beam direction is commonlyapplied to the ‘set of SRS port(s)’ configured in a specific Type 1 SRSresource, but the set of SRS port(s) may be transmitted in a form of“precoded SRS port” so as to apply specific digital beam directionswhich are different for each SRS port (for example, interpretable as theaforementioned class B UE related operation). Further, an additionaldigital beam direction is not applied to the ‘set of SRS port(s)’configured in the specific for each SRS port and the set of SRS port(s)may be transmitted while only the specific analog beam direction whichis commonly applied is already applied (for example, interpretable asthe aforementioned Class A UE related operation).

-   -   “Type 2 SRS resource” separated/distinguished from “Type 1 SRS        resource” described above may be defined or configured to the        UE. It can be seen (characterized) that the “Type 2 SRS        resource” is configured, for example, to        determine/change/configure/indicate a specific preferred        (analog) (Tx/Rx) beam direction for UL beam management.

In this case, one or more of Type 2 SRS resources may also be configuredto the UE. In this case, the UE may inform the base station of acapability of how many (Type 2) SRS resources may be configuredsimultaneously by UE capability signaling (at the time of initialconnection). It is preferable that the base station that receives thecapability provides configurations of a number not to violate thecapability.

One or more SRS port(s) may be configured in one Type 2 SRS resource.The UE may inform the base station of a capability (e.g., maximum value)of how many SRS ports(s) may be maximally configured per (type 2) SRSresource (and/or for each (Type 2) SRS resource) by the UE capabilitysignaling or the like (at the time of the initial connection). Inaddition, it is preferable that the base station that receives thecapability provides configurations of a number not to violate thecapability. And/or the UE may inform the base station of a capabilityfor the total number of SRS ports maximally supported throughout the(all) multiple (Type 2) SRS resources by the UE capability signaling orthe like (at the time of the initial connection). It is preferable thatthe base station that receives the capability provides configurations ofa number not to violate the capability. In this case, the capabilitysignaling may be defined or configured to the UE as a form (e.g., ajoint encoding form) to independently inform the base station of thetotal number of SRS ports maximally supported per (Type 2) SRS resource.

Through the UE capability signaling or the like, the UE may determineinformation related to the number (depending on the number of TXRUsimplemented by the UE) of (analog) beams that may be transmittedtogether at one time for UL beam management operations that may beimplemented/supported by the UE (in regard to Type 2 SRS resource).Therefore, there is an advantage/effect in that since a further UL beammanagement procedure is not operable, the base station determinesconfigurations of appropriate (Type 2) SRS resource(s)/port(s) byconsidering capability report information of multiple UEs based on afact that the UL beam management procedure is not operable to providethe determined configurations to the UEs.

Each configured (Type 2) SRS resource is a detailed configurationparameter and the UE may be limited in operation to transmit a set ofperiodically configured SRS port(s) (e.g., through RRC signaling and/orL2 (e.g., a MAC control element (CE)) signaling and/or L1 (e.g., DCI)signaling). Alternatively, the UE may be limited in operation totransmit a set of SRS port(s) in an “on-demand scheme” when triggered byaperiodically (by L1 signaling (by DCI).

Alternatively, such a periodic (Type 2) SRS resource and an aperiodic(Type 2) SRS resource may be mixed and configured to one UE. This hasthe advantage of having the highest configuration flexibility. In thiscase, information indicating whether the advantage is available may betransferred to the base station through specific UE capability signalingor the like in advance. Further, at least one of other SRS sequencegenerating parameter(s) (SRS sequence generating parameter(s), SRStransmit RE pattern information, comb-type related information, hoppingrelated information, and the like) may be configured for each (Type 2)SRS resource (independently).

For example, when one (Type 2) SRS resource is comprised of a single(OFDM) symbol (e.g., may be comprised of a periodic or aperiodicconfiguration), the UE may transmit (analog) beams of a number as manyas the number of panels or TXRUs of the UE at a correspondingtransmission time. In this case, the UE may be configured to repeatedlytransmit the SRS in multiple (OFDM) symbols (or specific sub-time units)for receiving beam scanning of the base station.

-   -   Consequently, when a situation in which at least one of the        above proposed contents is applied, for example, the UE may        assume a state in which Type 1 SRS resources #1, #2, and #3 and        Type 2 SRS resources #1, #2, #3, and #4 are configured (that is,        a total of 7 SRS resources are mixedly configured).

In this case, the UE may define whether to transmit the SRS port(s) towhich the same analog beam is applied in one SRS resource or the SRSport(s) to which different specific analog beams are applied (associatedwith which type of SRS resource is configured to the UE) or whether totransmit the SRS port(s) to which the same analog beam is applied in oneSRS resource or the SRS port(s) to which different specific analog beamsare applied may be indicated (configured) by the base station.

When the UE is defined/configured to transmit the SRS port(s) to whichthe same specific (analog) beam is applied in one SRS resource, this maycorrespond to the case where the Type 1 SRS resource (alternatively, theSRS resource may be configured in a form of the “Type 2 SRS resource” ormay be a specific SRS resource not classified as a specific type) isconfigured to the UE. It is characterized in that the UL beam managementand a UL CSI acquisition operation which is the “Type 1 SRS” relatedoperation may be simultaneously performed through transmission of thesingle specific SRS resource (for example, since the same beam isapplied to multiple ports, the base station is capable of deriving ULCSI).

On the contrary, when the UE is defined/configured to transmit SRSport(s) to which different specific (analog) beams are applied in oneSRS resource, this may correspond to the case where the Type 2 SRSresource is configured to the UE.

Herein, “specific” (analog) beam may be limited to a form in which aspecific beam directly indicated by the base station is applied. Forexample, in the case of the Type 1 SRS resource, the base station mayindicate to the UE a specific SRS port index within another specificType 2 SRS resource. That is, a scheme explicitly indicating to applythe (analog) beam applied to the corresponding SRS port index as it ismay be defined or configured to the UE. Alternatively, a scheme may beapplied in which the base station directly indicates to the UE with aspecific (analog) beam index. In this case, when the UE transmits theSRS on the precoded SRS resource, the SRS (e.g., Type 1 SRS) may betransmitted based on precoding (i.e., a precoder calculated on thecorresponding SRS) applied to another SRS (e.g., Type 2 SRS) indicatedby the base station.

And/or the “specific” (analog) beam allows the UE to arbitrarily apply aspecific beam base station-transparently and as described above, thecase of the Type 2 SRS resource may be limited to a fact that “differentspecific (analog) beams” that cover different regions need to be appliedbetween the SRS ports within the corresponding resource.

Further, herein, in respect to the case where it is defined orconfigured “so as to transmit the SRS port(s) to which the same specific(analog) beam is applied in the one specific configured SRS resource”,an application condition of such an operation may be further concrete.

For example, the operation of the UE may be defined or configured, whichindicates that “the same specific (analog) Tx beam should be applied tomultiple SRS ports that are transmitted at least at the same timeinstance (e.g., the same (OFDM) symbol) in one specific configured SRSresource”. This means that since the operation of the UE may beconfigured as such at least for a purpose of UL-MIMO link adaptation(CSI acquisition), the operation of the UE is defined or configured toapply the same specific (analog) Tx beam to multiple configured SRSports in this case. This may be limited only to multiple SRS ports thatare transmitted at the same time instance (e.g., the same OFDM symbol)as above (i.e., This may mean that the UE may be allowed/configured toapply another (analog) Tx beam together when specific SRS port(s)configured in the corresponding SRS resource are transmitted atdifferent time instances. Further, whether such an operation is alloweditself may follow a base station configuration.).

The UL-MIMO related operation may be variously applied/utilized bysingly defining only such definition/configuration(s). That is, thereason is that when it is desired to configure the SRS resource (or theSRS port(s)) for UL beam management purposes as the same purpose as theType 2 SRS resource, for example, a scheme in which multiple SRSresources in which a single port (or a small number of ports) isconfigured are configured may be applied (that is, since the UE mayapply different (analog) Tx beams between the SRS resources, a beammanagement operation may be implemented through the application of thedifferent (analog) Tx beams).

Therefore, the present invention proposes the following operations.

In NR UL, the SRS supports UE Tx beam sweeping and/or TRP Rx beamsweeping.

-   -   The UE may be configured as UE Tx beams different for each port        per SRS resource (for example, for U-2). Further, the UE may be        configured as the same UE Tx beam across ports per SRS resource        (for example, for U-3).    -   gNB may indicate the SRS port/resource selected for the UE.

Further, the present invention proposes the following operations.

For uplink CSI acquisition, multiple SRS resources may be configured inthe UE.

-   -   The UE may be configured to transmit the SRS port in the        configured SRS resource. Herein, at least two following options        may be used.

Option 1: The UE applies a gNB-transparent precoder (for example, the UEdetermines the Tx beam at each SRS port).

Option 2: The UE applies the precoder according to a gNB indication (forexample, the Tx beam for each SRS port is indicated by the gNB).

-   -   The gNB may indicate the selected SRS resource for the UE to        transmit uplink data on the same antenna port of the indicated        SRS resource.

A PMI (if indicated in the scheduling grant) for data transmission mayalso be applied across the antenna port.

Further, the present invention proposes the following operations.

For the uplink CSI acquisition, multiple SRS resources may be configuredin the UE.

-   -   The UE may be configured to transmit the SRS port in the        configured SRS resource. Herein, at least one of the following        alternatives may be used.

Alternative 1: The UE applies the gNB-transparent precoder (for example,the UE determines the Tx beam at each SRS port).

Alternative 2: The UE applies the precoder according to the gNBindication (for example, the Tx beam for each SRS port is indicated bythe gNB).

Alternative 3: Combination of Alternative 1 and Alternative 2 (e.g., thegNB indicates a set of precoders and the UE determines a subset ofprecoders).

-   -   The gNB may indicate the selected SRS resource for the UE to        transmit uplink data on the same antenna port of the indicated        SRS resource.

A PMI (if indicated in the scheduling grant) for data transmission mayalso be applied across the antenna port.

-   -   As described above, the UE may perform periodic SRS transmission        when the periodic type of the SRS resource is configured. For        periodic SRS transmission, the UE may be configured up to N SRS        resources. Further, the UE may be configured to transmit the N        SRS resources alternately at each transmission instance        corresponding to each transmission period or to defined or        configured to transmit the SRS by dividing the N SRS resources        based on the corresponding pattern by being configured a        specific pattern in advance (or separately).    -   Further, as described above, the UE may perform the aperiodic        SRS transmission when the aperiodic type of the SRS resource is        configured. For the aperiodic SRS transmission, the UE may be        designated to transmit the SRS of which SRS resource (e.g., an        SRS resource index or identifier (ID)) in the DCI triggering the        SRS transmission (i.e., may be explicitly indicated).    -   The operation of the UE may be defined/configured so that the UE        transmits the PUSCH by (by default) applying the (analog) beam        applied to which SRS port (index) (in the corresponding SRS        resource) of which (Type 2) SRS resource (and/or by applying        such (digital) beamforming together when there is additionally        indicated PMI related information) when the PUSCH scheduling.

As a result, as described above, even when the base stationconfigures/indicate for the UE to transmit the SRS on the SRS port forthe (Type 1) SRS resource, the base station may explicitly indicate forthe UE to transmit the SRS by applying the (analog) beam applied towhich (Type 2) SRS resource (or applied to which SRS port (index)(group) (in the corresponding SRS resource) as (analog) beam informationto be applied (by default) when transmitting the SRS on thecorresponding SRS port.

In other words, the base station may indicate to the UE (analog) beaminformation (that is, precoder/beamformer) used at the time oftransmitting the SRS on the SRS resource (e.g., Type 2 SRS resource)transmitted before the target SRS, when the base station indicates tothe UE (analog) beam information (that is, precoder/beamformer) to beapplied at the time of transmitting the target SRS on the target SRSresource (e.g., Type 1 SRS resource). That is, as linkage configurationinformation between the target SRS and the previously transmitted SRS,the base station may indicate to the UE the SRS resource informationthat is transmitted before the target SRS (for example, using the SRI orthe like).

Further, in more detail, specific SRS port (or SRS port group)information for the SRS resource (e.g., Type 2 SRS resource) that istransmitted before the target SRS may be indicated to the UE as the(analog) beam information (that is, precoder/beamformer) to be appliedat the time of transmitting the target SRS. That is, as linkageconfiguration information between the target SRS and the previouslytransmitted SRS, the base station may indicate to the UE the specificSRS port (or SRS port group) information in the SRS resource that istransmitted before the target SRS. Further, the base station mayexplicitly indicate that the UE transmits the PUSCH by applying the(analog) beam applied to which SRS port (index) (group) (in thecorresponding SRS resource) of which (Type 2) SRS resource (and/or byapplying such (digital) beamforming together when there is additionallyindicated PMI related information) at the time of the PUSCH schedulingas (analog) beam information to be applied (by default) at the time oftransmitting the corresponding PUSCH, even when configuring/indicatingthat the UE transmits UL data (that is, PUSCH) SRS on the correspondingSRS port.

Further, the base station may explicitly indicate that the UE transmitsthe PUSCH by applying the (analog) beam applied to which (Type 1) SRSresource transmission (and/or by applying such (digital) beamformingtogether when there is additionally indicated PMI related information)at the time of the PUSCH scheduling as (analog) beam information to beapplied (by default) at the time of transmitting the correspondingPUSCH, when configuring/indicating that the UE transmits UL data (thatis, PUSCH) SRS on the corresponding SRS port. That is, by indicating theType 1 SRS resource, it is possible to instruct to transmit the UL datain a scheme of linking the specific Type 2 SRS resource/ports that isalready applied thereto.

In such a specific explicit indication, a control message may betransferred to the UE by L1 signaling (e.g., by the DCI) and/or L2signaling (e.g., by MAC CE). Further, as described above, controlinformation may be transferred to the UE in a form of paired informationof a specific form such as (“SRS resource index/ID (with specific typeindication)” and “port index in indicated SRS resource orport-selection-codebook-index”). In this case, in order to comply withthe scheme indicated in the specific form of“port-selection-codebook-index”, a specific selection codebook forcomplying with the scheme may be defined in advance or configured to theUE and in the specific selection codebook, a specific codebook index maybe indicated. For example, the size of each code-vector is equal to thenumber of ports in the corresponding SRS resource, and each code-vectormay be defined or configured in a structure in which only one specificelement is 1 and all other elements are zero.

In the operations, indication information to perform transmission byapplying the specific (analog) beam applied to the specific (Type 2) SRSresource (or SRS port/port group) transmission indicated in the linkageform as it is may be defined/configured as a form to apply thecorresponding “latest specific (analog) beam applied to the “specific(Type 2) SRS resource (or SRS port/port group) transmission” withrespect to the time (e.g., transmitted in an nth (#n) time index) ofreceiving the corresponding indication information and/or the previoustime. Alternatively, a specific time point is specified, and as aresult, the indication information may be defined or configured, forexample, in the form to apply the (analog) beam applied to the latest(e.g., in specific Nth transmission before the latest transmission) withrespect to #n−k (e.g., may be set in advance/independently of candidatevalues such as k=0, 1, 2, . . . ) time and/or the previous time.

The following technologies are discussed in association with NR UL/DLMIMO.

At least one of the precoded SRS and the non-precoded SRS based on theUL link adaptation procedure is supported in NR at least using thefollowing different procedures.

The uplink data scheduling (MCS/precoder/rank) is based on non-precodedSRS transmission by the UE.

The number of configurable SRS ports is 1, 2, 4, or 8.

The uplink data scheduling (MCS/precoder/rank) is based on precoded SRStransmission by the UE.

The number of configurable SRS ports is 1, 2, or 4.

(If supported) multiple precoded SRS resources may be configured.

The precoder for the SRS may be determined by the UE based on themeasurement of the DL RS. Alternatively, the precoder for the SRS may beindicated by the gNB.

-   -   The uplink data scheduling (MCS/precoder/rank) is based on the        combination of the non-precoded and precoded SRS transmissions        by the UE.

Some of the procedures described above may be transparent to the UE.

-   -   For the purpose of the discussion, the classification        ‘closed-loop’/‘closes-loop’ is replaced with method-based        classification of ‘precoding and ‘precoder cycling’.

Signaling and UL-CSI measurements are supported to be processedseparately.

Precoding and precoder cycling may be considered for UL DMRS-basedspatial multiplexing (SM).

For a CP-OFDM waveform, a space frequency block code (SFBC) may becovered by a standard specification.

-   -   When the transmission port is greater than a predetermined X,        frequency selective precoding is supported for UL MIMO with the        CP-OFDM waveform.

The following example may be discussed.

Example 1

Precoding information for a given partial bandwidth (BW) is explicitlyindicated by the gNB.

The precoding information may be indicated through a hierarchicalindication as wideband W1 and subband W2.

W1 and W2 may be signaled with one DCI or two individual DCIs.

Example 2

A single beam group in the UL codebook is indicated by the base station(BS) for UL transmission in terms of the system bandwidth.

Example 2a

Precoder cycling is employed within the beam group.

Example 2b

The UE has specific flexibility in determining which specificbeam/precoder in the beam group for actual transmission.

Example 3: Reciprocity Based Precoding

-   -   The NR-SRS resource is comprised of a set of resource elements        (REs) and N antenna ports (N≥1) within a time duration/frequency        span.

The UE may be configured with K (K≥1) NR-SRS resources.

The maximum value of K may be determined in consideration of the UEcapability.

Hereinafter, based on the above discussion, UL-MIMO and precodedSRS-based transmission with the frequency selective precoding will bedescribed.

1) Frequency Selective Precoding

In order to apply frequency selective precoding for UL-MIMO in NR,control channel overhead which increases due to indicating subbandPMI(s) may be a serious problem. Although it may be considered to signalmultiple PMIs separately from the UL-related DCI and to include apointer field in the DCI for indicating such signaling, this kind oftwo-step approach may not be desired due to latency for providing thefull information of subband-wise multiple PMIs as a first step. In otherwords, a motivation of introducing such frequency selective UL precoderis to achieve fast UL link adaptation exploiting the frequency domain aswell, so that the full set of precoder information is desired to bedelivered instantaneously to the UE when the set of precoder informationis scheduled for the UL transmission. Thus, to support the frequencyselective UL-MIMO precoding identified in the above discussion, thefollowing options are proposed.

-   -   The precoding information may be indicated through a        hierarchical indication method by using the wideband W1 and the        subband W2.    -   W1 and W2 may be signaled within one DCI.

More specifically, in order to solve a control channel overhead issuefor frequency selective UL-MIMO scheduling, it is necessary to considerapplying a dual codebook structure to the UL case similar to DL (forexample, 4 transmission (Tx) case). The UL precoder W for each finalsubband may be decomposed into the wideband PMI element W1 and thecorresponding subband PMI element W2. In addition, in the UL schedulingDCI, it is sufficient that W1 information is included once and it isrequired that multiple W_2 are included according to the scheduledresource block (RB) given by the resource allocation field in the sameDCI. Although further discussion is needed as to how to define thecodebook for W1 and W2, it may be essential to re-use the release(Rel)-12 DL 4-Tx codebook. The existing LTE 2-Tx DL codebook may bereused for the 2-Tx UL case and the whole per-subband PMIs need to beprovided in the UL scheduling grant.

Accordingly, the full subband UL-MIMO precoder needs to be provided tothe UE in the UL scheduling grant and the wideband element may beincluded once to reduce control channel overhead.

2) Precoded SRS Based Transmission

For UL link adaptation (LA), LTE may support the UE to transmit the SRSwith different multiple sets of SRS related parameters, where the UE mayadopt precoding/selection on the SRS port(s) according to theimplementation of the UE especially when the configured number of SRSport(s) is smaller than the UE's total transmit (Tx) antenna ports.Compared to Rel-13/14, enhanced full-dimension MIMO ((e)FD-MIMO)beamformed CSI-RS based operations, precoded/beamformed SRStransmissions for UL LA need to be thoroughly investigated in NR.Similar to two types of DL CSI-RS resources (i.e., Type 1 for MIMO CSIfeedback and Type 2 for DL beam management), two different types of SRSresources need to be defined. That is, type 1 SRS resources for UL LAand SRS resources for UL beam management.

Thus, for purposes of different operations, it is desirable that twodifferent types of SRS resources are defined in NR. That is, type 1 forUL LA and type 2 for UL beam management.

In particular, for Type 1 SRS resources for UL LA, three classes ofoperations may be defined in terms of the UL LA process as follows.

Class A (UL-LA Based on Non-Precoded SRS Transmission)

The UE may be configured with one Type 1 SRS resource for the UE totransmit the non-precoded SRS.

Based on measuring UE's transmitted non-precoded SRS resource(s), theTRP determines the MCS and/or the precoder across the SRS port(s) andindicates the MCS and/or the precoder when the UL scheduling isdelivered to the UE.

In the case of 4-Tx UE and CP-OFDM, the above dual codebook structure isused for the frequency-selective UL-MIMO precoder.

Class B (UL-LA Based on Precoded SRS(s) Transmission)

One or more type 1 SRS resources may be configured in the UE.TRP-indicated beamforming or TRP-transparent beamforming is applied forthe SRS transmission on each SRS resource.

-   -   Based on measuring UE's transmitted precoded SRS resource(s),        the TRP determines SRS resource indicator (SRI) in case of        multiple configured SRS resources, MCS, and/or precoder across        the SRS ports within the SRI, and indicates the SRI, the MCS,        and/or the precoder when UL scheduling grant is delivered to the        UE.    -   Class C (UL-LA initiated with transmitting a non-precoded SRS,        and after that, transmitting a precoded SRS according to TRP's        indication)

Based on UE's transmitted non-precoded SRS K_1 port(s), the TRPdetermines coarse beamformer and indicates the determined coarsebeamformer to the UE to be applied on transmitting the followingprecoded SRS K_2 (≤K_1) ports(s). Then, based on UE's transmittedprecoded SRS port(s), the TRP determines MCS and/or precoder, andindicates the MCS and/or the precoder when UL scheduling grant isdelivered to the UE.

Based on the above classified classes for which the capability may bereported by UE, different UL-LA process may be configuredUE-specifically, including which classes of SRS transmission isperformed by the UE (e.g., Class B and/or Class C) and multiple type 1SRS resources may be configured to UE, where the UE transmitsdifferently-beamformed SRS port(s) on each configured SRS resource. TheTRP may indicate such beamformer information to the UE, or the UE isallowed to apply the TRP-transparent beamformer for the SRStransmission. Then, when UL scheduling grant is given to the UE, the TRPmay indicate the SRS resource indicator for which the UE should applythe same beamformer used on the SRS transmission corresponding to theindicated SRS resource, for the scheduled UL transmission. Further, onthe selected SRS resource, the TRP may further indicate digitalprecoding information (e.g., UL PMI) over the SRS port(s) in theindicated SRS resource. The configured number of SRS ports for each SRSresource may be interpreted as a target rank in UE's UL transmission.Therefore, the TRP may configure multiple type 1 SRS resources, eachcorresponding to the different rank (e.g., v-port SRS configured forv-th type 1 SRS resource, where v=1, 2, 3, 4, to cover rank 1 to 4).

Accordingly, procedures related with the non-precoded and/or precodedSRS transmission needs to be further discussed based on different UEtypes in terms of the UL link adaptation process.

When Type 2 SRS resources for UL beam management are configured in theUE and multiple SRS ports are configured in the resource, differentanalog beams need to be applied to the configured SRS ports to supportUL beam management. For example, when it is assumed that each SRStransmission instance includes a single OFDM symbol for a configuredType 2 SRS resource with P SRS ports, the UE needs to apply P differentanalog beam directions to different SRS ports, respectively andsimultaneously transmits the SRSs every SRS transmission instance. Inthis example, the UE may be implemented with P TXRUs/Panels, and thus,the value of P or related information needs to be initially delivered tothe gNB as a UE capability signaling such that appropriateconfigurations may be applied on appropriate type 2 SRS resource(s) forUL beam management.

After measuring transmitted SRS ports in Type 2 SRS resource, gNB mayselect preferred analog beam(s) to be used for applying to Type 1 SRSresource(s) or directly applying to some UL data transmissions to bescheduled.

As a result, NR should support mechanisms on UL beam management toindicate preferred beam(s) selected by gNB after measuring transmittedSRS ports in Type 2 SRS resource, to be applied on Type 1 SRSresource(s) or UL data transmissions to be scheduled.

The UL-MIMO scheduling by the DCI may include at least one of thefollowings.

SRS Resource Indicator (SRI)

In this case, this field may exist only when multiple SRS resources areconfigured to UE. As a result, the field may be defined to selectivelyexist so that the corresponding SRI field may be configured only in sucha specific condition (for example, when two or more (Type 1) SRSresources are configured, etc.).

Alternatively, the gNB may explicitly configure the existence of thecorresponding SRI field through the higher layer signal (e.g., RRCsignaling).

The bit width of the SRI field may be determined automatically (i.e.,implicitly) by ceil{log 2(N)} bits, assuming that the total number ofSRS resources (Type 1) SRS resources configured to the corresponding UEis N or determined by the configuration of the base station. Herein,ceil{x} means a function that outputs the smallest integer not smallerthan x.

Transmit Rank Indicator (TRI)

As the value of the field, up to the number of SRS ports configured inthe indicated SRI in the same DCI is available.

Transmit PMI (TPMI)

The precoding matrix (PM) depends on the number of SRS ports configuredin the indicated SRI in the same DCI.

This field may exist only when a codebook-based UL-MIMO scheme isconfigured to the UE. As a result, the field may be defined toselectively exist so that the corresponding TPMI field may be configuredonly in such a specific condition (for example, in the case of thecodebook-based UL-MIMO mode/operation, etc.). Alternatively, the gNB mayexplicitly configure the existence of the corresponding TPMI fieldthrough the higher layer signal (e.g., RRC signaling).

Further, even for non-codebook-based UL-MIMO cases, a selection codebookmay be used for the TPMI field.

-   -   UL MCS indication    -   UL Resource allocation

1) Operation for Codebook (CB) Based UL

Method 1) In the case of codebook-based UL, only one SRS resource setmay be configured.

-   -   One SRS resource is selected in the set via the SRI field in the        UL grant.    -   The SRI field in the UL grant is encoded at least independently        of the TPMI in the same UL grant.

The bit width of the SRI field is determined as N=ceil(log 2(number ofSRS resources in the set)).

As such, the SRI field may be designed in such a manner that theindicated target of the SRI field that may be indicated (by UL grant) inthe PUSCH scheduling is defined only to the SRS resource(s) in thespecific SRS resource set. That is, the SRI field may be the SRSresource set in which only Type A SRS resources (for CSIacquisition/link adaptation) are configured.

-   -   The SRS resource set may also be reused in UL beam management        (BM). Alternatively, separate SRS resource sets for the UL BM        may be configured to the UE.

For example, in the case of SRS resource set #1 in which the Type A SRSresources are configured, it is assumed that SRS resource set #2 (forexample, set #2 configured by grouping Type B SRS resources) separatelyconfigured for the purpose of the UL BM or the like is separatelyconfigured. In this case, in order to determine the SRI field size(length) as N=ceil(log 2(number of SRS resources in the set)), the UEneeds to clearly know for which SRS resource set to set only resourcesbelonging to the corresponding SRS resource set as a calculation target.

Thus, to this end, a separate indicator to indicate for which “set” tocalculating the N value may be configured or indicated from the basestation.

Further, for which “set” to calculate the N value may be implicitlydetermined by a specific (predetermined) rule/definition. For example,if the configured lowest SRS resource set (set #1 in the example above)is a target for calculating/applying the N value and the resultinggenerated 2{circumflex over ( )}N state description (e.g., each state isa state in which one of all configured CSI-RS resources is selected).

Method 2): The gNB may configure the N bit SRI state description for theUL grant by the RRC. Herein, regardless of whether the state descriptionis configured in the same or different SRS resource sets, each statedescription may include an SRS resource identifier(s).

Method 3) In the case of the codebook-based UL, multiple SRS resourcesets may be configured in the UE.

-   -   Only one SRS resource may be configured in each SRS resource        set.    -   Only one SRS resource (in the set) may be selected via the SRI        field in the UL grant.    -   The SRI field in the UL grant may be encoded at least        independently of the TPMI in the same UL grant.

The bit width of the SRI field is determined as “N=ceil(log 2(number ofSRS resources))”.

Similar to the case of Method 1 above, the UE is clearly aware that theType A SRS resources are gathered together to constitute the “number ofSRS resource sets containing only one SRS resource”, while the SRI fieldsize may be determined as “N=ceil(log 2(number of SRS resources))”.

Another separate SRS resource set(s) for the UL BM may be configured tothe UE.

2) Operation for Non-Codebook (Non-CB) Based UL

Method 1)

One SRS resource set may be configured in the UE.

Each SRI state may correspond to a predetermined combination of SRSresources configured in the SRS resource set for the non-CB based UL.

The bit width of the SRS field in the UL grant may be determined as“ceil(log 2(S_tot))”. Herein, S_tot may be defined as Equation 20 below.

$\begin{matrix}{S_{tot} = {\sum\limits_{k = 1}^{L_{\max}}\;\begin{pmatrix}N \\k\end{pmatrix}}} & \lbrack {{Equation}\mspace{14mu} 20} \rbrack\end{matrix}$

Herein, ceil{x} represents a function that outputs the smallest integernot smaller than x. N represents the number of SRS resources in the SRSresource set and S_tot represents the number of possible combinationsamong the SRS resources in the SRS resource set. L_max represents themaximum number of layers supported for the non-CB based uplinktransmission.

Another separate SRS resource set(s) for the UL BM may be configured tothe UE.

For example, in the case of SRS resource set #1 in which the Type A SRSresources are configured, it is assumed that SRS resource set #2 (forexample, set #2 configured by grouping Type B SRS resources) separatelyconfigured for the purpose of the UL BM or the like is separatelyconfigured. In this case, in order to determine the SRI field size(length) as N=ceil(log 2(S_tot)), the UE needs to clearly know for whichSRS resource set to set only resources belonging to the correspondingSRS resource set as a calculation target.

Thus, to this end, a separate indicator to indicate for which “set” tocalculate the N value may be configured or indicated from the basestation.

Further, for which “set” to calculate the N value may be implicitlydetermined by a specific (predetermined) rule/definition. For example,if the configured lowest SRS resource set (set #1 in the example above)is a target for calculating/applying the N value and the resultinggenerated 2{circumflex over ( )}N state description (e.g., each state isa state in which one of all configured CSI-RS resources is selected).

Method 2): The gNB may configure the N bit SRI state description for theUL grant by the RRC. Herein, each state description may include the SRSresource identifier(s) (up to the maximum L_max identifiers (IDs)) inthe set.

The CB-based UL mode and the non-CB-based UL mode themselves describedabove may be configured/switched by the higher layer. Therefore, whenthe “lowest set” is determined, if the current CB-based UL is available,the lowest set may operate to be the Type A target set and if thecurrent non-CB-based UL is available, the corresponding lowest set mayoperate to be the Type A target set. In this case, the lowest is just anexample and may correspond to ‘highest’ or specific‘predefined/determined indexed’ set.

The following UL-MIMO CSI acquisition class may be defined.

Class A (Non-Precoded)

The UE may be configured with one SRS resource with M(>1) ports, whichis non-precoded.

The UL scheduling grant may include at least TRI, TPMI, and MCSindication.

Class B (Beamformed)

The UE may be configured with k(>1) SRS resources having M_k(>1) ports,respectively, which is beamformed.

The UL scheduling grant may include at least SRI, TRI, (TPMI), and MCSindication.

Class C (Hybrid)

The UE may be configured with either {first class A+second class B} or{first Class B+second Class B}.

As described above, in the latter case {first class B+second class B},the first class B may be configured, for example, among the Type 2 SRSresources. In this case, the first class B may be limited to beconfigured only in the Type 2 SRS resource.

For example, if four resources of K=4 are configured in the first classB, the base station may receive the SRS transmission and select thespecific optimal resource(s), and then indicate to apply the selectedresource(s) to coefficients beamformed to the SRS resource(s) of thesecond class B. This corresponds to “indication of TX beam(s) capturedfrom the first class A/B to be applied to the second class B” to bedescribed below. When such an indication is provided, the UE may applythe Tx beam applied with respect to a single instance corresponding thelatest instance among instances prior to T time instance (e.g., T>=0)from the time when the indication is received as the corresponding Txbeam(s).

Such indication may be delivered by L2 (e.g., MAC CE) or by an aperiodicSRS trigger (e.g., DCI) for the second class B. The indication by theMAC CE means notifying to which specific (second class B) SRS resourceto apply the TX beam(s) (and/or a specific codebook beam vector appliedbetween the corresponding ports) applied to any specific SRS resourcethrough the corresponding message by scheduling a data header part inwhich the MAC CE may be transmitted (for example, by specific (DLrelated) DCI). Alternatively, the base station may notify theinformation together through the aperiodic SRS triggering DCI for thesecond class B.

The UL scheduling grant may include at least SRI, TRI, (TPMI), and MCSindication.

Hereinafter, a more detailed operation of a hybrid (i.e., Class C) willbe described.

If a form of {first class A+second class B} is configured, the“indication of Tx beam(s) captured from the first class A/B to beapplied to the second class B” may be an indication in a specific TPMIform. In this case, a dimension of the TPMI may be defined or configuredin a form that a specific value is indicated in a precoding matrix (PM)index having a dimension of a form (here, indicating a dimension of amatrix of the number of rows by the number of columns) of {the number ofports in the SRS resource corresponding to the first class A} by {thenumber of ports in the specific SRS resource of the applicable secondclass B}.

At this time, if the UE already receives how many the number of portsper each resource is included in the SRS resource (s) corresponding tothe second class B and the like, the dimension of the matrixcorresponding to the several-by-several may be determined automatically.Thus, if the above-mentioned indication is provided in the form of aspecific PM index value, the UE can apply the corresponding value amongthe PM candidate groups corresponding to the determinedseveral-by-several. As a result, when the PM is generally defined in aform of the number of ports-by-the number of layers, the informationindication of the TPMI type may also be interpreted as the fact thatinformation of applying Tx beam(s) is provided by considering as manylayers (or ranks) as the number of ports configured in the correspondingSRS resource of the second class B.

In addition, while the information of the number of ports in thecorresponding SRS resource of the specific second class B to be appliedmay be omitted from the upper layer (e.g., RRC) configuration parameteror defined to be ignored even if it exists, information of a specificTRI type may also be provided to the UE together with the TPMI as theindication information. In this case, as described above, the number ofSRS ports corresponding to the TRI value indicated at this time may bedefined or configured in a form that varies in association with theindication information of the configuration of the number of SRS portsin the form of being configured in association with the correspondingSRS resource of the specific second class B. As such, considering thatthe number of ports in the SRS resource of the second class B can bevariable, a location of the SRS transmission resources varying accordingto the determined number of ports may be defined or configured inadvance so that the allocation of the SRS transmission resource may bevariable.

The above description is not limited to only the operation of the classB, but may be applied to all methods (operations) of applying thespecific Tx beam(s) information described in the present invention tothe specific beamformed/precoded SRS resource.

Next, if a form of {first class A+second class B} is configured, the“indication of Tx beam(s) captured from the first class A/B to beapplied to the second class B” may be an indication in a specific SRIform (and/or SRI and specific port(s) of the corresponding SRI). In thiscase, it may be regarded as a form that indicates to apply the Txbeam(s) applied to the corresponding SRI and/or port index(s) to thecorresponding SRS resource of the corresponding specific second class B.If such an indication is defined or configured in a form of indicating aspecific SRI and the number of ports in the corresponding SRI and thenumber of ports configured in the corresponding SRS resource of thespecific second class B are the same as each other, the indication maybe defined or configured so that the same Tx beam is applied for eachport. If the numbers of the ports are different from each other, atleast one of the following several options may be applied with respectto how to be processed:

The UE can assume that the same Tx beam applied to the indicated SRI inthe indicated first class B is applied to all the ports in the SRI andcan apply the assumption to the second class B.

The UE may assume that a different Tx beam is applied for each port inthe indicated SRI in the indicated first class B. In addition, amongthem, the UE may arbitrarily select the Tx beam and apply the selectedTx beam to the corresponding SRS resource of the second class B. Thisindicates that the indication to the SRI for the first class B is toinform the Tx beam groups as many as the number of ports, and in thiscase, the UE supports the operation to be selected and appliedgNB-transparently and by itself.

As another method, in a state in which the information on the number ofports in the corresponding SRS resource of the specific second class Bto be applied is omitted from the upper layer (e.g., RRC) configurationparameter or defined to be ignored even if it exists, when the specificSRI is indicated as the indication information, it may be regarded thatthe number of SRS ports in the SRI indicated at that time is as many asthe number of SRS ports in the corresponding to SRS resource of thespecific second class B. That is, the configuration of the number of SRSports may be defined or configured in a variable form by interlockingwith the indication information. As such, considering that the number ofports in the SRS resource of the second class B can be variable, alocation of the SRS transmission resources varying according to thedetermined number of ports may be defined in advance or configured sothat the allocation of the SRS transmission resource may be variable.Alternatively, if the SRI is indicated, a period (e.g., 50 ms) in whichthe corresponding SRI is transmitted in the first class B is preciselychanged to a predetermined period (e.g., 10 ms) with respect to thecorresponding SRS resource of the second class B, and the SRStransmission resource location may be applied to be transmitted to thesame transmission resource location of the corresponding SRI in thefirst class B. Until a next-changed SRI indication is received from amoment when it is transmitted in a long-term (e.g., 50 ms) and thenindicated to the SRI before being selected as SRI among the SRSresources in the first class B, this may be applied as an operation(e.g., 10 ms set for the second class B) that varies the SRStransmission period corresponding to the indicated SRI. That is, even inthe case of semi-persistent and/or aperiodic SRS, the periodic/aperiodictransmission type may be over-ridden to the periodic/aperiodictransmission type configured in the second class B. This description isnot limited to the class B operation, but can be applied to all theoperations (methods) of applying the specific Tx beam(s) informationdescribed in the present invention to the specific beamformed/precodedSRS resource.

-   -   UL-MIMO scheduling by DCI may include at least one of the        followings:

i) Indication (SRI) of the SRS resource that has been transmitted by theUE at the previous time instance

Each configured SRS resource is associated with at least one UL Txbeam/precoder.

This field may also exist only when multiple SRS resources areconfigured to the UE.

ii) Transmission rank indicator (TRI)

The value of this field can be up to the number of SRS ports set in theindicated SRI.

iii) Broadband transmission PMI (TPMI)

The precoding matrix PM depends on the number of SRS ports configured inthe indicated SRI.

This field may not be present for non-codebook UL MIMO transmission.

iv) UL MCS indication

Method 1 and Method 2 may be supported as follows when the Tx beamformerfor SRS is determined.

i) Method 1: The UE applies a Tx beamformer to the SRS in a gNBtransparent manner (e.g., the UE determines the Tx beam for each SRSport/resource).

i) Method 2: Determined based on gNB indication (via SRI).

Transmission for codebook based UL will be described.

The codebook-based UL transmission includes at least the followingsignaling in the UL grant:

i) SRI+TPMI+TRI

Here, TPMNI is used to indicate a preferred precoder over the SRSport(s) in the SRS resource selected by the SRI.

ii) If a single SRS resource is configured, there is no SRI.

iii) In the case of a multi-panel, a set of {SRI+TPMI+TRI} may besupported for each panel.

Additional precoding indications (e.g., co-phasing over multiple SRSresources) and the like may be considered over the multiple SRSresources.

iv) Selection in the multiple SRS resources may be indicated to supportfrequency selective precoding. For example, each of indicated SRI 1, SRI2, SRI 3, . . . may be limited to be applied only to specific(predefined or configurable) frequency granularities (e.g., groups ofPRB and the like). As a result, frequency selective precoding in afrequency domain can be applied by multiple SRIs.

SRI Signaling for SRS Tx Beam Determination

For application to the SRS Tx beam for SRS resources for UL CSIacquisition, the SRI is selected from the SRS resources for theconfigured UL beam management.

The SRI may be indicated as DCI or MAC CE.

At this time, the SRS port index may be indicated together with the SRI.

Here, the SRI is different from the SRI included in the UL grant.

-   -   Non-codebook based UL transmission for UL supports at least the        following signaling in UL grant.

i) SRI without TPMI/TPI

The rank is equal to the sum of the set number of SRS port(s) over oneor more SRS resource(s) selected by the SRI.

For data transmission, the UE applies the same precoder(s) as theprecoder(s) used in the SRS port(s) indicated by the SRI to a PUSCHport(s).

The selection of multiple SRS resources may be additionally instructedto support frequency selective precoding.

ii) If a single SRS resource is configured, there is no SRI.

Non-periodic SRS triggering field in UL related DCI

i) N-bit field

The first codepoint corresponds to ‘SRS transmission is not triggered’.

The n-th codepoint selects at least one of the configured SRS resources.Thus, one or more SRS resource(s) may be jointly encoded for each statein each SRI field. At this time, each state or codepoint is described inadvance in the RRC/MAC CE, and the corresponding state may be indicateddynamically.

ii) This field is an independent SRI field.

FIG. 14 is a diagram illustrating an uplink transmission/receptionmethod according to an embodiment of the present invention.

Referring to FIG. 14, the UE receives uplink reference signal (e.g.,SRS) resource configuration information from a base station (S1401).

The uplink reference signal (e.g., SRS) resource configurationinformation is used to configure the transmission of the uplinkreference signal, and the configuration includes uplink reference signalresource set(s) information and uplink reference signal resource(s)information in each uplink reference signal resource set. In particular,the uplink reference signal resource configuration information mayinclude a linkage configuration (that is, linkage information) betweenan uplink reference signal, which is a target of the correspondinguplink reference signal resource configuration information, and anuplink reference signal (e.g., SRS)/downlink reference signal (e.g.,CSI-RS) transmitted before the corresponding uplink reference signal.

Here, the linkage configuration means indication information whichperforms (e.g., application of the same precoder/beamformer)transmission of a target uplink reference signal (e.g., SRS) based on aprecoder/beamformer that has been applied to the specific uplinkreference signal/downlink reference signal resource/port transmission.Although only the uplink reference signal is illustrated in FIG. 14, thepresent invention is not limited thereto.

At this time, as the linkage configuration information between thetarget uplink reference signal (the second uplink reference signal inFIG. 14) and the uplink reference signal (the first uplink referencesignal in FIG. 14)/downlink reference signal which has been transmittedbefore the corresponding uplink reference signal, the uplink referencesignal/downlink reference signal resource information which has beentransmitted before the target uplink reference signal may be indicatedto the UE (e.g., using SRI and the like).

In addition, as the linkage configuration information between the targetuplink reference signal (the second uplink reference signal in FIG. 14)and the uplink reference signal (the first uplink reference signal inFIG. 14)/downlink reference signal which has been transmitted before thecorresponding uplink reference signal, the base station may alsoindicate specific antenna port (alternatively, antenna port group)information to the UE.

In this case, the specific uplink reference signal (the first uplinkreference signal in FIG. 14) may correspond to the most recentlytransmitted uplink reference signal before the transmission of thetarget uplink reference signal (the second uplink reference signal inFIG. 14).

The UE transmits the precoded first uplink reference signal to the basestation (S1402).

The UE transmits the precoded second uplink reference signal to the basestation on the uplink reference signal resource indicated by the uplinkreference signal resource information in step S1401 (S1403).

That is, the UE may be configured with one or more uplink referencesignal resource sets, and one or more uplink reference signal resourcesin the set may also be configured. Therefore, in step S1401, the uplinkreference signal resource configuration information may be indicated notonly for each first uplink reference signal but also for the seconduplink reference signal. However, for convenience of description, in thepresent embodiment, it is described that the uplink reference signalresource configuration information in step S1401 is assumed asinformation on the second uplink reference signal (i.e., the seconduplink reference signal is a target reference signal).

At this time, the UE may transmit the second uplink reference signalbased on the precoding (i.e., precoder/beamformer) applied to the firstuplink reference signal indicated by the linkage configurationinformation. For example, the precoding applied to the first uplinkreference signal can be equally applied at the time of transmitting thesecond uplink reference signal.

As described above, the UE may be configured one or more uplinkreference signal resource sets, and one or more uplink reference signalresources in the set may also be configured. At this time, the basestation may configure which operation the uplink reference signalresource is used.

For example, the uplink reference signal resource may be classified intoa Type 1 uplink reference signal resource (for link adaptation) and aType 2 uplink reference signal resource (for beam management) asdescribed above. The base station may notify to the UE whether theconfigured uplink reference signal resource (or the resource set) is theType 1 uplink reference signal resource or the Type 2 uplink referencesignal resource. Alternatively, the base station may notify to the UEwhether the configured uplink reference signal resource (or the resourceset) is the uplink reference signal resource of link adaptation or theuplink reference signal resource for beam management.

General Apparatus to which the Present Invention May be Applied

FIG. 15 illustrates a block diagram of a wireless communicationapparatus according to an embodiment of the present invention.

Referring to FIG. 15, the wireless communication system includes a basestation (eNB) 1510 and a plurality of user equipments (UEs) 1520 locatedwithin the region of the eNB 1510.

The eNB 1510 includes a processor 1511, a memory 1412 1512 and a radiofrequency unit 1513. The processor 1511 implements the functions,processes and/or methods proposed in FIGS. 1 to 14 above. The layers ofwireless interface protocol may be implemented by the processor 1511.The memory 1512 is connected to the processor 1511, and stores varioustypes of information for driving the processor 1511. The RF unit 1513 isconnected to the processor 1511, and transmits and/or receives radiosignals.

The UE 1520 includes a processor 1521, a memory 1522 and a radiofrequency unit 1523. The processor 1521 implements the functions,processes and/or methods proposed in FIGS. 1 to 13 above. The layers ofwireless interface protocol may be implemented by the processor 1521.The memory 1522 is connected to the processor 1521, and stores varioustypes of information for driving the processor 1521. The RF unit 1523 isconnected to the processor 1521, and transmits and/or receives radiosignals.

The memories 1512 and 1522 may be located interior or exterior of theprocessors 1511 and 1521, and may be connected to the processors 1511and 1521 with well known means. In addition, the eNB 1510 and/or the UE1520 may have a single antenna or multiple antennas.

The embodiments described so far are those of the elements and technicalfeatures being coupled in a predetermined form. So far as there is notany apparent mention, each of the elements and technical features shouldbe considered to be selective. Each of the elements and technicalfeatures may be embodied without being coupled with other elements ortechnical features. In addition, it is also possible to construct theembodiments of the present invention by coupling a part of the elementsand/or technical features. The order of operations described in theembodiments of the present invention may be changed. A part of elementsor technical features in an embodiment may be included in anotherembodiment, or may be replaced by the elements and technical featuresthat correspond to other embodiment. It is apparent to constructembodiment by combining claims that do not have explicit referencerelation in the following claims, or to include the claims in a newclaim set by an amendment after application.

The embodiments of the present invention may be implemented by variousmeans, for example, hardware, firmware, software and the combinationthereof. In the case of the hardware, an embodiment of the presentinvention may be implemented by one or more application specificintegrated circuits (ASICs), digital signal processors (DSPs), digitalsignal processing devices (DSPDs), programmable logic devices (PLDs),field programmable gate arrays (FPGAs), a processor, a controller, amicro controller, a micro processor, and the like.

In the case of the implementation by the firmware or the software, anembodiment of the present invention may be implemented in a form such asa module, a procedure, a function, and so on that performs the functionsor operations described so far. Software codes may be stored in thememory, and driven by the processor. The memory may be located interioror exterior to the processor, and may exchange data with the processorwith various known means.

It will be understood to those skilled in the art that variousmodifications and variations may be made without departing from theessential features of the inventions. Therefore, the detaileddescription is not limited to the embodiments described above, butshould be considered as examples. The scope of the present inventionshould be determined by reasonable interpretation of the attachedclaims, and all modification within the scope of equivalence should beincluded in the scope of the present invention.

INDUSTRIAL APPLICABILITY

The present invention has been described based on an example in which itis applied to the 3GPP LTE/LTE-A systems or 5G system, but may beapplied to various wireless communication systems in addition to the3GPP LTE/LTE-A systems or 5G system.

The invention claimed is:
 1. A method of performing uplink reception bya base station (BS) in a wireless communication system, the methodcomprising: transmitting configuration information for a first soundingreference signal (SRS) that specifies a relation between the first SRSand a second SRS that is a reference for spatial beamforming of thefirst SRS; and based on the configuration information for the first SRSspecifying the relation between the first SRS and the second SRS:receiving the first SRS transmitted by applying, to the first SRS, afirst spatial beamforming that is identical to a second spatialbeamforming used for transmission of the second SRS, wherein the methodfurther comprises: transmitting downlink control information (DCI) foruplink scheduling, wherein the DCI comprises a SRS resource indication(SRI); and wherein a SRI field in the DCI carries the SRI, and wherein abit width of the SRI field is based on a number of SRS resources in anSRS resource set configured for a user equipment (UE).
 2. The method ofclaim 1, wherein the configuration information for the first SRSspecifying the relation between the first SRS and the second SRScomprises (i) resource information for the first SRS or (ii) antennaport information for the first SRS.
 3. The method of claim 1, whereinreceiving the first SRS comprises performing an operation that isconfigured by the base station.
 4. The method of claim 3, wherein theoperation comprises an uplink data scheduling operation and a beammanagement operation.
 5. The method of claim 4, wherein the firstspatial beamforming is applied to the first SRS for the uplink datascheduling operation so as to form beams of the same direction in allSRS antenna ports configured in a single SRS resource.
 6. The method ofclaim 4, wherein the first spatial beamforming is applied to the firstSRS for the beam management operation so as to form beams of differentdirections for each SRS antenna port configured in a single SRSresource.
 7. The method of claim 1, wherein receiving the first SRScomprises: periodically receiving or aperiodically receiving the firstSRS based on triggering by the DCI.
 8. The method of claim 1, whereinthe second SRS, which is the reference for spatial beamforming of thefirst SRS, is an SRS that was most recently transmitted by the UE beforetransmitting the first SRS.
 9. The method of claim 1, wherein the bitwidth is based further on a maximum number of layers supported foruplink transmission, and wherein the bit width of the SRI field is basedon an equation:┌log₂ s _(tot)┐ wherein ┌⋅└ represents a ceiling function, wherein${S_{tot} = {\sum\limits_{k = 1}^{L_{\max}}\;\begin{pmatrix}N \\k\end{pmatrix}}},$ wherein N represents the number of SRS resources inthe SRS resource set configured for the UE, and wherein L_(max)represents the maximum number of layers supported for the uplinktransmission.
 10. The method of claim 1, further comprising: performingan uplink reception on an SRS antenna port that is transmitted in an SRSresource that is selected by the SRI.
 11. The method of claim 10,wherein performing the uplink reception comprises: performing the uplinkreception based on a non-codebook based transmission.
 12. The method ofclaim 1, wherein the configuration information for the first SRSspecifies the relation between the first SRS and the second SRS byidentifying the second SRS as a reference SRS for the first SRS.
 13. Abase station (BS) configured to perform uplink reception in a wirelesscommunication system, the BS comprising: a transceiver; at least oneprocessor; and at least one computer memory operably connectable to theleast one processor and storing instructions that, when executed, causethe at least one processor to perform operations comprising:transmitting configuration information for a first sounding referencesignal (SRS) that specifies a relation between the first SRS and asecond SRS that is a reference for spatial beamforming of the first SRS;and based on the configuration information for the first SRS specifyingthe relation between the first SRS and the second SRS: receiving thefirst SRS transmitted by applying, to the first SRS, a first spatialbeamforming that is identical to a second spatial beamforming used fortransmission of the second SRS, wherein the method further comprises:transmitting downlink control information (DCI) for uplink scheduling,wherein the DCI comprises a SRS resource indication (SRI); and wherein aSRI field in the DCI carries the SRI, and wherein a bit width of the SRIfield is based on a number of SRS resources in an SRS resource setconfigured for a user equipment (UE).
 14. An apparatus configured toperform uplink reception in a wireless communication system, theapparatus comprising: at least one processor; and at least one computermemory operably connectable to the least one processor and storinginstructions that, when executed, cause the at least one processor toperform operations comprising: transmitting configuration informationfor a first sounding reference signal (SRS) that specifies a relationbetween the first SRS and a second SRS that is a reference for spatialbeamforming of the first SRS; and based on the configuration informationfor the first SRS specifying the relation between the first SRS and thesecond SRS: receiving the first SRS transmitted by applying, to thefirst SRS, a first spatial beamforming that is identical to a secondspatial beamforming used for transmission of the second SRS, wherein themethod further comprises: transmitting downlink control information(DCI) for uplink scheduling, wherein the DCI comprises a SRS resourceindication (SRI); and wherein a SRI field in the DCI carries the SRI,and wherein a bit width of the SRI field is based on a number of SRSresources in an SRS resource set configured for a user equipment (UE).